Six The Pantheon Builders: Estimating Manpower for Construction

Janet DeLaine

Introduction

The Pantheon has long had iconic status, universally acknowledged as the greatest achievement of Roman architecture and one of the wonders of the Roman world. The unparalleled clear span of the dome particularly impressed later architects and engineers, who used it as a point of reference for their own wide-span structures, including the domes of Santa Maria del Fiore in Florence, St. Peter’s in Rome and St. Paul’s in London, and even the great Victorian train sheds of St. Pancras Station.1 A major part of the universal fascination with the building lies in its complex structural system and the constructional processes employed, particularly in relation to the dome.2 Because of the difficulties we have with understanding the Pantheon as a structure, it has been natural to imagine that it was also an exceptionally difficult, time-consuming, and labor-intensive construction project for the Romans. The aim of this chapter is to test some of these assumptions, using a method of reverse quantity surveying, originally developed for the Baths of Caracalla in Rome.3 This can provide a rough estimate of the minimum manpower requirements for the actual construction on site (excluding all labor relating to the production, supply, and transportation of materials to the site), as well as the minimum construction period. Although the calculations can yield only approximate and hypothetical minimum figures, they at least provide an idea of the scale of the project in terms of manpower, and allow us to test whether this really was the “mammoth undertaking” assumed by many scholars.4 This also has implications for how we see the Pantheon as part of the building projects of Trajan and Hadrian.

Construction Analysis

The first requirement in estimating manpower is an understanding of the physical fabric in order to calculate volumes of materials and assign human actions to putting them into place. In essence, the Pantheon, as can be seen in the set of line drawings published by Kjeld De Fine Licht (Figs. 6.16.5), consists of a circular drum (the rotunda), divided in plan into eight piers by alternately rectangular and semicircular recesses. This drum supports a dome that is roughly hemispherical in profile on the inside, while the exterior of the drum is divided into three zones (lower, middle, and upper), the upper zone rising to approximately one-third of the height of the dome. On the entrance side there is a rectangular structure (the intermediate block), which links the rotunda to the columnar pedimented portico forming the main facade. The intermediate block is also divided by cornices into three registers, equivalent to the three exterior zones of the drum. At the opposite end, at the rear of the rotunda, is a series of parallel barrel-vaulted chambers (thegrottoni) built between the Pantheon and the probably contemporaneous Basilica of Neptune to the south (Fig. 6.5).5 The Pantheon once sat at the head of acolonnaded precinct, but this will not be included in the calculations here. While it is not necessary for the purpose of this exercise to describe the whole of the fabric of the building in detail, some explanation will be givenfor the assumptions and approximations used where evidence is limited or details are open to various interpretations.


6.1. Ground plan. (Licht 1968, Fig. 98)


6.2. Half plans of upper levels. (Licht 1968, Fig. 97)


6.3. Half sections through the rotunda. The annotations refer to different types of aggregate, for which see Fig. 1.12. (Licht 1968, Fig. 99)


6.4. Longitudinal section. (Licht 1968, Fig. 105)


6.5. Isometric rendering from rear, showing the so-called grottoni (grottoes), the Basilica of Neptune, and the triple-arched connection or “bridge” between the two at high level. (Licht 1968, Fig. 175)

The Rotunda, Intermediate Block, and Grottoni

The rotunda and intermediate block, while not entirely without difficulty, are the easiest parts of the Pantheon to analyse in terms of construction and have been the parts most discussed in the literature.6 Much less has been written about the grottoni, but the basic construction of the lower parts is virtually identical to that of the Rotunda. All walls are made of a uniform brick-faced concrete, with approximately 70 pieces of brick per square meter of facing, based on the average size of the brick pieces and the mortar joints. The materials of the core are less easy to measure and, as is well known, the caementa (rubble aggregate) in the rotunda change through its height. Nevertheless, the size of the pieces of rubble does not necessarily change, remaining roughly fist sized, and what evidence we have suggests that an average figure of 5,000 pieces of caementa per meter cubed is a sensible assumption.

The brick arches, which are such a feature of the external face of the drum, are an important part of the structure of the rotunda; following earlier scholars, these are assumed to pass through the whole thickness of the drum and be made of solid brick, although this has in fact never been proven.7 These and most of the other arches that appear on the face of the structure are made of bipedales, although a few of the smaller ones are of sesquipedales. The bridge above the grottoni rests on a solid brick vault of very similar construction. Also of bipedales are the level courses of bricks (the so-called bonding courses), which run right through the thickness of the fabric at regular intervals. At more than 25 kilograms each, bipedales require careful handling and cannot be laid at the speed of ordinary bricks, a point that also needs to be taken into account in the calculations.

The construction of both the brick-faced concrete and the arches can be broken down into simple actions carried out by individual masons, and all of the materials that need to be put in place – bricks, rubble aggregate, mortar – are sufficiently small and light to be carried by individuals as well, most probably in baskets. The only exception is the main interior order of the rotunda, which requires a very different range of materials and skills that are more difficult to quantify. Stone working needs specialized labor, and most elements, particularly the monolithic marble shafts weighing more than 20 tonnes each, need special equipment and large teams of men to raise and guide into position.

The most difficult element for analysis is the dome. The basic fabric, especially up to the top of the step-rings visible on the exterior, is little different from that of the drum of the rotunda, and similar skills and actions were required for putting the concrete in place, although the caementa are larger and lighter so that 4,000 pieces per meter cubed is a better estimate. The real difficulties lie in attempting to reconstruct the formwork and centering used to support the concrete while it cured, which in turn affects the sequence of construction. Since there is no consensus about this among scholars, and to argue the case is beyond the scope of this study, here it is assumed that the lower part of the dome up to the top of the drum is cantilevered out and does not require full centering (see Chapter Seven), but that the upper part of the dome from the top of the level of the drum is erected as a series of rings over a complete centering.

The Portico

The same kinds of skills required for the erection of the interior order of the rotunda are also necessary for the traditional masonry construction of the portico (see Fig. 1.1 and Plate I). The demands here are greater, however, since the elements are heavier (the 40-Roman-foot granite column shafts weigh more than 50 tonnes each), and the heavy blocks of the entablature and tympanum need to be raised to greater heights, involving even more specialized equipment and even larger groups of men. The main problem with understanding the portico construction, however, is that the current supports for its roof are not ancient. The roof has been much altered since antiquity, acquiring its present state in the 1920s, leaving many questions still to be resolved.8 Although sufficient drawings of the ancient bronze trusses that were robbed in the 1620s remain for a basic reconstruction,9 the roof may have been part of the restoration program of Septimius Severus,10 leaving open the strong possibility that the bronze trusses are Severan and that the older roof was of a more traditional timber construction.11 Even if the bronze trusses were original, reconstructing the manpower figures for their manufacture and construction, if indeed possible at all, would require a separate study. Thus, the calculations here are based on a traditional timber truss structure similar to the current system but with marble roof tiles.12

Groundwork, Foundations, and Substructures

The least straightforward elements of the overall construction to assess are the groundworks and foundations, so that any result can only be a broad approximation. The foundations of the portico incorporated substantial amounts of an earlier ashlar building, presumed to be part of the original Agrippan Pantheon, which were partly reworked to support the front row of columns, while new concrete foundations were created for the side and internal rows.13 In contrast, earlier structures were removed rather than reused from the foundation trenches for the grottoni, as for the rotunda itself, before the concrete was laid (see Fig. 2.6).

Since the portico of the present Pantheon lies about 1.4 meters higher than its predecessor, and its internal floor was closer to 2 meters higher than before, the earlier building need only have been demolished to roughly the new higher level, not to its foundations. This would have saved time and manpower. On the other hand, allowance has to be made for raising the overall level of the internal floors of the whole building, creating further need for labor. This seems to have happened before the foundation trench for the present rotunda was dug, as the interior face of the foundation appears to have been cast in a trench to just below the current floor level (see Fig. 2.4 and Plate XVIII). This is in contrast to the upper part of the foundation externally, which is built of brick-faced concrete and higher than the external early second-century ground level, forming a low ring podium.


XIII. Visualization of the sequence of operations in building the Pantheon. (Model Mark Wilson Jones and Robert Grover)


XIV. Plan of Pantheon (in black) overlaid with reconstruction of Agrippa’s Pantheon (in red), according to Rodolfo Lanciani 1897


XV. Schematic reconstruction of Augustan Pantheon, according to Gerd Heene 2004.


XVI. Aerial view of alignment between Pantheon and Mausoleum of Augustus. (P. Vergili, “Scavi in piazza della Rotonda e sulla fronte del Pantheon,” in Grasshoff, Henzelmann, and Wäfler 2009, Fig. 10)


XVII. Pantheon, reconstruction views, intended (below) and as executed (below). (Model John Burge)


XVIII. Plan of 1891–1892 excavations. Red arrows point to trenches exposing earlier floor. (Beltrami 1898)


XIX. Composite section combining information from excavations under portico and rotunda. (Drawing Giovanni Joppolo)


XX. Section detail of 1891–1892 excavations illustrated in Figure 2.3, looking toward pilaster framing east side of entrance portal. (Pier Olinto Armanini in Beltrami 1898)

The nature of the foundations raises further problems. Although it is widely presumed that the foundations of the rotunda are about 4.5 meters deep and rest on clay, the situation is in fact more complex. The upper part, forming the podium externally, is about 2 meters above the early second-century ground level, and thus structurally more part of the building than of the foundations, which implies that the foundations proper would be only 2.5 meters deep. It is also clear from Armanini’s summary drawing of the late nineteenth-century excavations of the Pantheon foundations that most of these are cut into a constructional fill, as the natural clay lies slightly below the base of the earlier travertine wall under the portico. From the foundations of other major Roman buildings of similar height, such as the Flavian Amphitheatre (ca. 7 meters into alluvium and bedrock plus ca. 6 meters of substructures), the Baths of Caracalla (6.5 meters into clay plus 8 meters of substructures), or the Domitianic Triclinium on the Palatine,14 we would expect the foundations to be deeper in themselves and bedded further into the underlying natural geology. Even minor buildings such as the Trajanic/Hadrianic insulae at Ostia, at approaching half the height and a fraction of the span of the Pantheon, often have foundations more than 3 meters deep extending into the subsoil.

These known examples can be compared with the few indications we have in the written sources. Vitruvius gives no rules for determining the depth of foundations except that for temples they should be proportionate to the size of the work, and should extend “into the solid” (de arch. 3.4.1). Palladius (1.8.2), writing in the fourth century in relation to villas, recommends that foundations in solid clay need to be one-fifth to one-sixth of the total height of the building, while those in loose earth need to be dug until solid clay is found, or to a total height of one-quarter of the building. The early medieval Mappae Claviculae, generally argued to be based on earlier Roman building practice, recommends that the depth of foundations for vaulted structures should equal the height of the walls to the springing of the vault.15 The obelisk of Augustus’s solarium north of the Pantheon in the Campus Martius was reputed to have had foundations equal to its height of 22 meters (Pliny, Naturalis Historia 36.72–73); while this figure cannot be taken as entirely reliable, it does suggest that the foundations were considerable. These figures suggest a possible range for the depth of foundations from 7 to 9 meters up to 22 meters. Given how limited the excavations of the rotunda foundations have been, it is in fact quite likely that they were much deeper than the 4.5 meters generally presumed.16

For the purpose of this exercise, it will be assumed that the depth of the foundation below the podium is 7 meters, the minimum of the range suggested by these sources, which is also in keeping with figures for the Flavian Amphitheatre and the Baths of Caracalla, and no allowance will be made for labor saved by reusing earlier structures. This will give a very rough estimate only, but might at least provide an order of magnitude. The figures that can be calculated for the foundations are for digging and filling those of the rotunda, the intermediate block, and the grottoni, constructing the external brick face of the podium, and creating the new foundations for the inner columns of the portico.

Calculating the Manpower: Assumptions, Approximations, and Limitations

The estimates of manpower given here are based on a volumetric analysis of the main parts of the structure, derived from the dimensions given by Licht, where necessary scaled from plans and sections he supplies,17 while taking into account the factors outlined in the previous section. Supplementary information derives from the recent laser survey conducted by the Karman Center in Bern (Fig. 6.6). In order to avoid excessively complicated calculations (e.g., in relation to precise forms of arches), an idealized geometry has been employed, mainly in the assumptions that all curves are parts of circles, spheres or cones.18 Based on experience from calculations for the Baths of Caracalla, small openings (2 meters wide or less) have been ignored, as the work required to form them in thick walls roughly equates to work saved. This should allow quantities of materials to be calculated to a reasonable degree of accuracy.


6.6. Laser scan of longitudinal section. (Karman Center, Bern, BDPP0021)

Nevertheless, several other assumptions, approximations, and limitations have to be made to arrive at manpower estimates, relating both to the fabric of the building and to the conditions of labor. As we have seen, some elements of the foundations, the roofing of the portico, and the centering for the dome structure have had to be excluded, or only a very rough estimate given, because there are simply too many unknowns. Also excluded from the calculations are most preliminary groundworks; the preparation of materials away from the site, including quarrying, lime burning, and brick production; the transport of materials to the site and the removal of construction debris; and any waste of materials, which might have added upward of 10 percent in terms of mortar alone. Minor elements of the main fabric, for example the brick and travertine external cornices, have also been excluded. Apart from the labor required for shaping and setting up of the columnar orders of the rotunda and the portico, which is an essential part of the construction process, decoration and finishing will be discussed only very briefly. On the other hand, aspects of the construction process that are not immediately obvious in the finished fabric often require large amounts of labor and have been included, such as processing materials on site, moving building materials horizontally and vertically to where they are required to be put in place, erecting scaffolding, and formwork. Also taken into account is supervision at rates of 1:10 for most construction, and 1:4 or 5 for complex actions such as raising and setting in place the architectural orders or erecting large formwork.

Other assumptions affect the operation of the building site and have direct implications for labor requirements. Once the building materials have arrived on site, they need to be stored until needed, with some elements requiring further processing, such as lime slaking and mortar mixing. The most likely areas for this are in the open space to the north, which later became the Pantheon precinct, and the area of the Saepta Iulia alongside the Pantheon to the east, which, according to the evidence of brickstamps, was rebuilt immediately after the Pantheon.19 The internal area of the rotunda may also have been used in the early stages of construction. The availability of such large spaces in the immediate vicinity suggests that horizontal movement of materials on site could be reduced to a minimum, and an average figure of 50 meters is assumed in the calculations. Finally, it is assumed that no extra work was necessary for the furnishing of the construction infrastructure – the cranes, pulleys, ropes, scaffolding, and baskets essential to the construction process – as all of this, including special large cranes and equipment needed for moving and putting in place large architectural elements and formwork, would presumably have been available either in imperial stores or with imperial contractors involved with previous large-scale building works, such as the Baths of Trajan and the Forum of Trajan completed in AD 109 and AD 112/113, respectively.20 Even much of the timber for the formwork should have been readily available from the same sources, although some extra work would be necessary to adapt this to current needs.

The manpower constants needed to convert volumes of materials into the amount of labor required for construction are derived from historic figures for labor output in the building trades, in particular data from nineteenth-century Italy where traditional methods of construction and building materials comparable to those of the Roman period were still in use.21 The particular figures and formulae used have been chosen to match as closely as possible the process of construction and specific working conditions that can be identified from traces left in the fabric of the Pantheon, or, where this is not possible, from more general observations of contemporary Roman construction in brick-faced concrete. From the consistency of rates for laying bricks from different periods and/or places, for example, it is reasonable to assume that this would have been very similar in the Roman period when similar tools were used, suggesting a figure of 500 bricks per day for a mason, for actually laying the face of the Pantheon, with an assistant to supply the bricks and mortar.22

A number of assumptions have had to be made about how these relate to ancient working practices, but these are all slanted toward providing minimum figures for labor, on the understanding that the actual figures are likely to have been higher.23 The specific assumptions used here concerning working conditions are those used for the labor estimates relating to the Baths of Caracalla. The historical labor constants are given for an hour’s work, over a day of 10 working hours (12 hours including breaks), and it is assumed that the ancient working day was the same. All labor here has been treated as the same, although it would be possible at a later stage of analysis to divide it into unskilled and a variety of skilled trades (e.g., masons, carpenters, marble workers).

Since it is not possible to make accurate allowance for all of the uncertainties inherent in the exercise, these calculations provide only approximate and hypothetical figures, which serve as a guide to the scale of operations rather than any kind of precise values for the actual situation in antiquity.24 In addition, the figures as calculated are generally minimum possible figures, while the exigencies normal to building operations in all periods strongly suggest that actual figures would have been higher.

Since the building divides neatly into four virtually separate elements, it is simplest to present the raw manpower figures as four tables, each divided into the relevant number of construction phases or processes.

Altogether, the calculations suggest that a minimum of about 400,000 (399,000) mandays were required for the main phases of construction of the Pantheon, comprising 340,000 mandays of general construction labor (rotunda 272,900; intermediate block 30,400; porch 7,300; grottoni 26,000) plus about 60,000 mandays for shaping the architectural elements (see Tables 6.1, 6.2, 6.3, and 6.4). A more useful way of expressing this data in order to assess the historical significance of a building project is as a number of men working over a given time: the figures given here for the Pantheon are the equivalent of 1,100 men working every day for a year, or 110 men for 10 years. If, however, we take into account the likely actual sequence of construction along with attendant practical considerations, it should be possible to estimate more precisely the minimum size of the workforce and the shortest possible period over which it was required.

Table 6.1. Manpower for building the rotunda in mandays (mdays) of labor


Rotunda

 

Foundations

Lower zone

Middle zone

Upper zone

Dome

Total

Quantities

             

Total volume (m³)

 

9,490

7,050

6,710

8,070

5,180

36,500

Brick pieces in facing

 

24,000

365,000

178,000

136,000

178,000

881,000

Actions

Rate

Total mdays

Total mdays

Total mdays

Total mdays

Total mdays

Total mdays

Excavate in rocky ground to 1.6 ma

0.165 mdays/m³

320

       

320

Excavate 1.6 m

0.248 mdays/m³

782

       

782

Remove debris over 50 mb

0.164 mdays/m³

1240

       

1,240

Slake lime for mortarc

1.2 mdays/m³

771

535

426

586

437

2,760

Mix mortard

0.55 mdays/m³

1,950

1,290

1,310

1,860

1,340

7,750

Fetch materials

0.164 mdays/m³

1,560

1,160

1,100

1,320

850

5,990

Lay foundationse

0.384 mandays/m³

5,350

       

5,350

Lay facef

800 (1,000*) pieces/day x 1.5 for assistant

36*

684

332

254

 

1310

Lay coreg

4.01 + 0.12 (ht – 1) mdays/m³ x 1.5 for assistant

8,440

40,300

38,400

67,500

 

154,500

Lay core for dome

2.68 + 0.08 (ht – 1) mdays/m³ x 1.5 for assistant

       

53,500

53,500

Lay arches and bonding coursesh

200 bricks/day x 1.5 for assistant

 

240

1,010

591

67

1,910

Raising materialsi

0.12 mdays/m³ x (ht – 1)

 

700

3,410

3,100

1,350

8,560

Erect scaffoldingj

0.063 mdays/m² face

 

334

206

334

300

1,170

Formwork for vaultsk

0.2 (0.4*) mdays/m²

 

27

470

799

1,740*

3,040

Subtotal

 

20,500

45,300

46,700

76,300

59,600

248,000

Supervision

10% of total

2,050

4,530

4,670

7,630

5,960

24,800

Shaping orders

   

16,900

2,470

   

19,400

Moving and lifting ordersl

   

1,480

756

   

2,240

TOTAL

 

22,500

68,200

54,600

84,000

65,600

295,000


a Pegoretti 1869, vol. 1, pp. 240–245, for the whole process of digging foundations.

b Pegoretti 1869, vol. 1, p. 157.

c Pegoretti 1869, vol. 2, p. 131.

d Pegoretti 1869, vol. 2, p. 144.

e Pegoretti 1869, vol. 2, p. 144.

f DeLaine 1997, no. 3, pp. 268–269, note 5. The higher figure indicated by an asterisk is for the rougher brickwork in the substructures.

g Pegoretti 1869, vol. 2, pp. 144–145.

h Pegoretti 1869, vol. 2, p. 156, and DeLaine 1997, no. 3, p. 176.

i Pegoretti 1869, vol. 1, p. 243.

j Pegoretti 1869, vol. 2, pp. 6–7, for all details of scaffolding.

k Pegoretti 1869, vol. 2, p. 209, for all details of vault centering. The higher figure is for the more complex vaults.

l Pegoretti 1869, vol. 2, pp. 14–15.

Table 6.2. Manpower for building the intermediate block in mandays (mdays) of labor


Intermediate block

 

Foundations

Lower zone

Middle zone

Upper zone

Total

Quantities

           

Total volume (m³)

 

933

1,340

1,175

509

4,000

Brick pieces in facing

 

3,420

64,300

52,600

57,000

177,000

Actions

Rate mdays/m³

Total mdays

Total mdays

Total mdays

Total mdays

Total mdays

Excavate in rocky ground to 1.6 m

0.165 mdays/m³

37

     

37

Excavate below 1.6 m

0.248 mdays/m³

175

     

175

Remove debris over 50 m

0.164 mdays/m³

153

     

153

Slake lime for mortar

1.2 mdays/m³

99

104

143

67

412

Mix mortar

0.55 mdays/m³

249

250

439

206

1,140

Fetch materials

0.164 mdays/m³

199

220

748

352

1,520

Lay foundations

0.384 mdays/m³

196

     

358

Lay face

800 pieces/day x 1.5 for assistant

5

121

177

29

332

Lay core

4.01 + 0.12 (ht – 1) mdays/m³ x 1.5 for assistant

1,240

7,810

9,040

4,260

22,400

Lay arches and bonding courses

200 bricks/day x 1.5 for assistant

 

34

20

30

84

Raising materials

0.12 mdays/m³ x (ht – 1)

 

114

487

229

830

Erect scaffolding

0.063 mdays/m² of face

 

59

50

54

163

Formwork for vaults

0.2 mdays/m²

 

11

28

27

66

Subtotal

 

2,520

8,720

11,100

5,250

27,600

Supervision

10% of total

250

870

1,110

525

2,760

TOTAL

 

2,770

9,590

12,200

5,780

30,400


Table 6.3. Manpower for building the portico in mandays (mdays) of labor


Portico

 

Foundations

Columns

Entablature

Pediment

Roof

 

Action

Rate

Total mdays

Total mdays

Total mdays

Total mdays

Total mdays

Total mdays

Excavate in rocky ground to 1.6 m

0.165 mdays/m³

38

       

38

Excavate below 1.6 m

0.248 mdays/m³

180

       

180

Remove debris over 50 m

0.164 mdays/m³

157

       

157

Slake lime for mortar

1.2 mdays/m³

78

       

78

Mix mortar

0.55 mdays/m³

198

       

198

Fetch materials

0.164 mdays/m³

157

     

3

160

Lay foundations

0.384 mdays/m³

368

       

368

Tie up blocks with ropesa

0.03/0.033 mdays/m³ x 5 men

 

88

52

56

32

228

Place on rollers

0.025/0.0275 mdays/m³ x 5 men

 

73

43

47

24

187

Move large items 50 m

0.003days/m x 50 m x (5 + (wt – 5t)/1.25) men

 

207

125

128

203

663

Raise and put in place

0.025 days/m x ht x (11 + wt/0.625) men

 

627

889

1,020

1,590

4,130

Lay roof

0.22 mdays/m3 + 1.625 mdays/m2

       

759

759

Subtotal

 

1,180

995

1,110

1,250

2,610

7,150

Supervision

10% of total

118

included

included

included

included

118

Shape stone and marble elements

   

33,600

4,940

1,620

 

40,200

TOTAL

 

1,300

34,600

6,050

2,870

2,610

47,500


a Pegoretti 1869, vol. 2, pp. 14–15, for this and all other formulae for moving and raising large blocks.

Table 6.4. Manpower for building the grottoni in mandays (mdays) of labor


Grottoni

 

Foundations

Lower zone

Middle zone

Upper zone

Total

Quantities

           

Total volume (m³)

 

1,070

1,330

1,260

526

4,190

Number of brick pieces in facing

   

91,200

89,000

57,000

237,000

Action

Rate mdays/m³

Total mdays

Total mdays

Total mdays

Total mdays

Total mdays

Excavate in rocky ground to 1.6 m

0.165 mdays/m³

43

     

43

Excavate below 1.6 m

0.248 mdays/m³

202

     

202

Remove debris over 50 m

0.164 mdays/m³

176

     

176

Slake lime for mortar

1.2 mdays/m³

87

105

98

28

318

Mix mortar

0.55 mdays/m³

222

319

304

89

934

Fetch materials

0.164 mdays/m³

176

218

202

86

682

Lay foundations

0.384 mdays/m³

412

     

412

Lay face

800 pieces/day x 1.5 for assistant

 

171

168

15

354

Lay corea

4.03 + 0.12 (ht – 1) mdays/m³ x 1.5 for assistant

 

7,870

8,400

3,260

19,530

Lay arches and bonding courses

200 bricks/day x 1.5 for assistant

 

45

15

98

158

Raising materials

0.12 mdays/m³ x (ht–1)

 

73

175

123

371

Erect scaffolding

0.063 mdays/m² of face

 

93

84

20

197

Formwork for vaults

0.2 mdays/m² of face

 

106

98

54

219

Subtotal

 

1,320

9,000

9,540

3,770

23,600

Supervision

10% of total

132

900

954

377

2,360

TOTAL

 

1,450

9,900

10,500

4,150

26,000


a Pegoretti 1869, vol. 2, pp. 144–145. The figure is slightly higher than for the rotunda because of the relative thinness of the walls.

Scheduling the Work

Construction on the whole is a logical process, where the sequence of events is largely determined by structural necessity, the inexorable demands of gravity, and the behavior of materials. Within these limits, however, there are usually several different ways in which the work can be scheduled, especially in complex projects like the Pantheon with its four potentially independent units. In addition, certain construction processes require the cessation of work for a period of time. As concrete gains strength only over time, it is not possible that the whole of the fabric of the rotunda could have gone up in a single season. The builders would have wanted to be sure that the strength of the concrete was sufficiently developed before laying the drum on the foundations, and before erecting the dome on the drum, making these obvious places for a fairly lengthy cessation of work. Additional stages are also highly likely, as argued later.

The first steps in construction are obviously the groundworks and foundations. The archaeological and constructional evidence suggests that all of the foundations of the rotunda, intermediate block, and portico were created at the same time, but that those of the grottoni, which abut those of the rotunda, were added partway through construction.25

While the sequence of construction for the rotunda itself is reasonably self-evident, a few points need to be made here. The first is that the three divisions, coinciding with the three exterior cornices, would appear to mark natural breaks in construction (Fig. 6.3). On the interior, the lowest corresponds with the top of the frieze of the main order. The insertion of the lower columnar order would have necessitated a hiatus in the construction of the drum, since the order is an integral part of the structure and both architrave/frieze and cornice blocks are embedded in its concrete walls. For these heavy marble blocks to be supported by the concrete, the drum probably needed to have gained more strength than ordinarily required to support the next lift of concrete, although exactly how long this would have taken cannot be determined.26 The same applies to the cornice blocks of the interior attic zone, which project strongly and thus need to be deeply embedded in the walls. Although the upper zone of the drum on the inside forms the lower part of the dome, this part is almost vertical and could easily have been built by gently cantilevering out each lift of concrete (see Chapters Four and Seven). The need for the whole drum and lower part of the dome to gain most of its strength before the upper part of the dome was added introduces another necessary hiatus in construction.

The situation is more complicated with the other three elements of the building, as, for example, the lower walls of the grottoni and the upper walls of the intermediate block abut the rotunda and must have been built later than it. Although the intermediate block was clearly planned as an integral part of the Pantheon, it is only bonded to the rotunda up to roughly the level of the first exterior cornice, so that the rest cannot have been completed until after the drum was finished.27 Since there are no structural reasons for the intermediate block not to be bonded to the rotunda, it is reasonable to assume that there was a gap of a season or more. Exactly how long after the rotunda was finished is impossible to determine, but the similarities in the brickstamps make it clear that not much time elapsed. The inverse situation prevails for the grottoni, where the structure seems not to have been part of the original plan, but was added partway through the construction of the rotunda, perhaps for structural reasons.28 Here, only the bridge is bonded to the rotunda, so that the lower and middle parts of the structure must have arisen only after the corresponding levels of the drum had already been completed. Again, the three levels of the grottoni do not necessarily represent different building phases. The final section to be built was the portico, which is independent of the rotunda and cannot be any earlier than the upper levels of the intermediate block, which are essential prerequisites for its construction. Current arguments for a change in design affecting the portico also assume that this was added last.29

Practical constraints also affect the size of the workforce and the time taken for construction, the kind of logistical considerations that are still an essential part of modern building practice. The construction period is limited by the length of the building season and the number of days when no building work is taking place. A recently discovered series of grafitti from the near-contemporary Baths of Trajan has provided a unique window on the actual working conditions prevailing on major imperial building sites in Rome.30 The sequence of dates painted roughly on the walls of the structure as it rose suggest that there were no rest days, and that the builders worked from at least late February to October. If we apply this work schedule, but allow for the constraints on construction due to adverse weather conditions in the winter months, then we can assume a construction season of 270 days over 9 months for outdoor work, with indoor work (some materials preparation, interior decoration) continuing over a 12-month season of 365 working days maximum.

The main logistical constraint on the speed of construction is the maximum number of men that can be assigned to any given task. The most important of these is the maximum number of masons that can be employed simultaneously along any given stretch of wall or foundation, which is largely determined by the physical geometry of the structure. While the Renaissance architect Filarete recommended a minimum spacing of masons of 1.85 meters, the average span of an adult male, the pattern of the grafitti from the complex semicircular exhedra of the Baths of Trajan implies a spacing of 3.5 meters, roughly twice that;31 given the much larger diameter and the fewer reentrant elements such as niches in the Pantheon, for this exercise a slightly closer spacing of 3 meters will be assumed. It would therefore not be feasible to fit more than about 100 masons working on the brick facings and core at the same time on any level of the rotunda, which suggests a minimum time for each of the first three levels of about 260 days; the external cornices of the rotunda therefore might each have represented the end of a single building season.32 In comparison, no stage of the intermediate block or the grottoni would need anything more than half a season; indeed, it would be theoretically possible to have built the middle or upper zone of the intermediate block, or the lower or middle zone of the grottoni, in less than 100 days each. The shortest possible theoretical schedule for the Pantheon would, therefore, be six years, assigning a year each to the site works, foundations and substructures; the lower zone of the rotunda and intermediate block; the middle zone of the rotunda and the foundations of the grottoni; the upper zone of the rotunda and all of the grottoni; the completion of the dome, the rest of the intermediate block and the portico; and the decoration. As Lise Hetland’s redating of the Pantheon based on the brickstamps33 provides a starting date of AD 112–114, this six-year schedule would suggest a possible completion date of AD 117–119.

The presence of dated brickstamps in the fabric of the Pantheon, however, enables us to refine this schedule and makes such an early completion date unlikely. The catalogue published by Bloch provides sufficient information to locate about 50 stamps with a reasonable degree of certainty.34 The stamped bricks are not distributed uniformly, but it is significant that stamps of Rutilius Lupus with secure consular dates of AD 114 and 115 occur in the middle zone of the rotunda, and those of AD 117 in the upper level of the grottoni, built together with the upper zone of the rotunda. This makes it certain that the dome itself must have been completed under Hadrian, but the total absence of clearly Hadrianic brickstamps, particularly those of AD 123, in the whole of the main fabric, including the dome and the upper part of the intermediate block, excludes a predominantly Hadrianic structure, as Hetland has also noted. On the other hand, studies of late Trajanic and Hadrianic structures at Ostia suggest that the majority of bricks tended to be used relatively soon after they were produced,35 so that it is reasonable to assume that work on the Pantheon had indeed begun by AD 114, rather than that these stamped bricks represent old stock. Assuming that the work could not begin before 112, and more likely 113, and allowing also for the construction pattern of the grottoni, which might have required a hiatus before work started on the upper zone of rotunda (see the section “Years 3–5: Completing the Rotunda and the Grottoni”), a minimum construction schedule over seven years, plus two for decoration, ending in AD 122, would be feasible. This proposed schedule could equally be spread over more years if there were any unforeseen breaks in construction, for example due to structural problems or delays in the supply of materials,36 but the absence of stamps of AD 123, except for one possible example behind the decoration in the porch, does not allow the schedule to be extended beyond a couple of years, finishing with the decoration in AD 123 or 125. This schedule provides a strong working hypothesis that can be used to assess the size of the workforce.

The Size of the Workforce

Calculating the size of the required workforce involves further assumptions, and can only produce average minimum figures. It is assumed that all of the labor works at full capacity for the whole of 10 hours per day, and that the required workforce is always available – neither being very likely if modern practice is any guide. It is also assumed that Roman contractors avoided extreme peaks in labor demands as far as possible, as happens in modern construction projects where they are considered weak points in the scheduling. This would have been particularly important where skilled workmen were concerned, for example, the marble workers preparing the stone for the orders. Such calculations and considerations are of course hypothetical, and many other schedules are possible, but the exercise at least allows us to establish some realistic minimum parameters for the work. The suggested figures are given in Table 6.5.

Table 6.5. Number of men required for a 9-year construction schedule


Year

Days

Portico

Intermediate block

Rotunda

Grottoni

Total

1

135

Groundworks

?

 

135

Foundations 10

Foundations 20

Foundations 170

 

200

2

340

   

Prepare orders 60

 

60

 

255

 

Lower level 40

Lower zone 190

 

230

 

15

   

Erect orders 100

 

100

3

40

   

Prepare cornice 60

 

60

 

80

   

Middle zone 230

 

230

 

20

     

Foundations 70

70

 

170

     

Lower and middle levels 135

135

4

160

   

Middle zone 230

Start bridge 10

240

 

15

   

Erect cornice 50

 

50

 

95

   

Start upper zone 230

Continue bridge 10

240

5

340

Prepare stone 60

     

60

 

270

   

Complete upper zone 230

Complete bridge 10

240

6

340

Prepare stone 60

     

60

 

270

 

Middle level 40

Dome to coffers 200

 

240

7

120

 

Upper level 50

Complete dome 90

 

140

 

130

Erect 50

     

50

8–9

 

Finish decoration

Finish decoration

Finish decoration

 

?


Year 1: Foundations and Site Preparation

If we assume that the making of the foundations for the portico, rotunda, and intermediate block occupied all of the first season of 270 days, only a relatively small number of men – roughly 100 – would have been required. The shortest possible time, determined by the maximum number of men who could work on the rotunda foundations at any time, would be about 90 days, needing 300 men each day. Neither of these figures, however, takes into account any of the preparatory groundworks, which could have occupied, say, half of the first season. In Table 6.5 it has, therefore, been assumed that the digging and laying of the foundations occupied only the second half of the season, that is, 135 days, requiring an average workforce of about 200 men each day, who might have spent the same sort of time in the preliminary groundworks.

At the same time, we need to allow for a break between laying the foundations proper and erecting the substructures above them, which could have been as much as several months while the concrete completed curing and gained strength. Although it may be that the proposed three months between the construction seasons would have been sufficient, we need to bear in mind that since the domed rotunda was pushing Roman construction technology to its limits, a longer period may have been considered necessary. Site preparation, for example, could have been carried out in one year and the foundations laid at the beginning of the next season. Some work could have progressed in the meantime, for example, lime slaking, which preferably had to be done at least three months ahead of the time needed,37 andthis period might also have seen the accumulation of materials in on-site depots ready for the major construction phases. Of course, the uncertainties over the details and extent of the foundations just discussed mean that the labor requirements given here are likely to be lower than they were in practice, just as the time period could easily have been longer. This all makes an actual starting date of the main part of the structure before AD 114 highly unlikely.

Year 2: The Lower Zones of the Rotunda and the Intermediate Block

The second year of the proposed schedule is probably the most secure, with the rotunda and intermediate block rising together. In this year it is also necessary to take into account the time required for erecting the columns and entablatures of the main interior order at the end of the season. As the entablature blocks over the columns of the recesses were embedded into the concrete walls of the drum on either side and supported in the center on the paired columns, the subsequent sequence of construction meant that they could not have been inserted later. The absolute minimum possible time for this, given that the elements have to be erected in sequence – base, column shaft, capital, architrave, frieze, and cornice – is about five days. If all were erected together this would require 14 teams of at least 11 skilled stoneworkers, each team with its own crane, plus a large number of men to provide the motive power for each (up to 40 in the case of the columns shafts). Given that the columns in each pair are quite closely spaced, however, one team for every pair of columns gives a more likely maximum number of teams, although only three or four would be feasible concurrently. If we leave, say, 15 days at the end of the 270-day season for this process, then there are only 255 days for erecting the masonry of the lower zone, needing just over 190 men (Table 6.5), approximately the same number as suggested for the foundations. The building of the lower zone of the intermediate block adds another 40 men, while 80 stone carvers would have been needed over the same period for preparing the architectural elements, if indeed this was done on site or nearby.38 It is also possible that work had started on these elements during the previous year, and a period of 340 days requiring on average 60 stone carvers is suggested here. Much would have depended on the availability of the large blocks needed, especially the column shafts, and this is therefore one of the more difficult elements for which to estimate the numbers of craftsmen required.

Years 3–5: Completing the Rotunda and the Grottoni

As the manpower requirements for the middle zone of the rotunda are very similar to those of the lower zone, requiring 215 men on average if spread over 255 days, in theory this could also have been completed in a year. A short period of 15 days has again been taken out of the 270-day season at the end of this construction phase to raise and put in place the interior cornice blocks, a simpler operation than installing the interior order but similarly requiring the blocks to be embedded in the concrete; using the same equipment this would have needed roughly 50 men. Preparing the blocks for this cornice could have been done by just 7 men over 365 days, or 60 men over 40 days if the team that had worked on the interior orders was used.

The building of the grottoni, however, adds a level of complexity to the scheduling, which is open to several possible solutions. While the foundations of the grottoni could have been dug and filled in as little as 20 days with 70 men, there is an upper limit of 135 men based on a 3 meter spacing of bricklayers at the face for each of the lower and middle ranges. This gives a minimum construction time of roughly 85 days for each of the two levels. Scheduling for this depends on the point at which the decision to add the grottoni arose. They are independent of the rotunda until about one-third of the way up the middle zone, and so one schedule might see the foundations of the grottoni begun at the start of the season, then being left to gain strength for, say, 80 days, while work continued on the middle zone of the rotunda, and then resume with the lower range of the grottoni, continuing without interruption with the middle range, and finishing after 190 days at the end of the season while the internal cornice was being added to the interior of the rotunda. In this schedule, the building of the grottoni is designed to operate in tandem with that of the rotunda, gradually catching up to end just behind it. This would produce the physical abutting of the grottoni that can be observed in the structure. It would mean, however, that the necessary workforce would have to have been more than half as large again as required for the lower zone of the rotunda, some 330 men.

If we accept, however, that the grottoni were an attempt to redress a perceived structural weakness in the drum,39 then it is likely that an extra year needs adding to the schedule. In this reconstruction, the fault would have manifested itself early in the third year of construction while the middle zone of the rotunda was being built. Work on the rotunda would have been suspended for at least 190 days, to build the foundations and then the first two levels of the grottoni, requiring only 135 men.

Work could have recommenced on the middle zone of the rotunda and the final level of the grottoni (the bridge) in the fourth season, requiring 240 men altogether over 160 days, plus 15 days for the interior cornice to be put in place. The scheduling at this stage is further complicated by the fact that manpower requirements increase and speed of construction decreases with height, because of the extra time and effort needed to get materials to their required positions, to erect scaffolding, and for the men themselves to move around the building. While it may appear natural to have waited until the following season to start building the upper zone of the rotunda, it would have been difficult to complete this section in a single season without greatly increasing the workforce. Even allowing for starting within the extra 95 days left at the end of the fourth season of construction, an average of 240 men would have been needed to complete the upper zone of the rotunda and grottoni in the 270 days of the fifth season. This would have given three months for the drum of the rotunda to gain strength before erecting the main part of the dome in the sixth season.

Years 6–7: The Upper Dome, Intermediate Block, and Portico

Rather different concerns affect the scheduling in the final stages of the work, in particular the sequence in which the building operations are carried out. One difficulty is that, unlike the walls of the drum where there would have been masons working at both internal and external faces, the upper part of the dome could only be laid from the external face, as there was a solid centering behind the internal face. This means, therefore, that only half the number of masons could have worked on the dome at any time compared with the number who worked on the drum. This problem is compounded by the fact that the length of the workface also decreases as the dome rises, so that while 58 masons could have worked at the outer face at the base of the upper dome, only 9 could have worked at the oculus with the assumed spacing of 3 meters. Work therefore necessarily slows down considerably as the dome enters its final stages, with the result that it is very unlikely to have been completed in a single season of 270 days, and a minimum period of 345 days would be a better estimate; about a third of that period would have been needed just for the final section above the coffers. A schedule that saw the dome built up to the end of the coffering in the sixth season would have required roughly 200 men, with 90 working on the final section in the first 120 days of the next season.

Such a schedule has some advantages. The lower two-thirds of the dome is both more vertical and, particularly with its stepped extrados, better able to contain any horizontal elements of thrust. By allowing it to gain strength over the winter, it would have become self-supporting, potentially allowing for the complex formwork and heavy scaffolding required for building the coffers to be removed before the crown was added. The lower dome would then have been much more effective in supporting the crown, constructionally the most difficult part of the operation due to its increasing horizontality, and structurally the part most at risk of failure for just the same reason. The relatively small and lightweight crown in turn could have been decentered toward the end of the seventh season. Removing the formwork for the dome in two stages in this way may have been easier than decentering such a vast span in a single action.

This still leaves the completion of the intermediate block, and here there are several possible solutions. The upper level could employ no more than 50 masons over a minimum period of 57 days, with an overall workforce of about 100 men. The solution suggested here is to build the middle level of the intermediate block with the lower part of the dome, using 40 men over the whole season. As the completion of the intermediate block is an essential prerequisite for the construction of the portico, the latest it could be completed, assuming the portico was begun in the seventh year, would have been at the same time as the crown of the dome was being built, with its much reduced workforce. Spread over the 120 days needed for finishing the dome, the final section of the intermediate block would have required only about 50 men.

Considerations of logistics are even more important when we examine the erection of the portico. Here it would be theoretically possible to put the whole of the portico colonnade in place in 9 days, with 230 men divided into 16 teams, raising each column and entablature sequence simultaneously. Given the relatively restricted amount of space available around each column, especially the internal ones, this is unlikely, and there would be additional problems in raising the roof trusses once all of the colonnade was in place. A more logical scheme would be to start erecting the colonnade from the rear against the intermediate block, putting in place first the marble piers and then the inner row of columns, followed by the corresponding entablatures and finally the first and second roof trusses over the piers and the columns. Work would then progress outward toward the facade, so that once the pediment was in place, the main supporting structure of the roof was already complete, and the actual roof timbers and marble tiles could be put in place. Even this would make it awkward to maneuver the larger blocks, especially the column shafts and architraves that needed two cranes, into place, particularly for the inner columns. Here it is assumed that only two columns or entablatures were erected at the same time, starting with the inner pair and moving outward. Similar considerations apply to the blocks of the pediment and its cornice. The columns and entablatures would then take a minimum of about 50 days, allowing for the cranes to be moved, with a further 0.5 day for each truss, and 11 days minimum for the pediment. The roof adds a further minimum of 30 days. If the same crew of 50 men were used throughout, the whole could be done in about 130 days, although more men would be needed at specific times to raise the largest blocks. Before this, all of the stonework (columns, entablatures, and roof tiles) would have needed to be prepared, which could have been done over two years of 340 days by the same 60 workmen who prepared the internal orders.

Years 8–9: Decorating and Finishing

The final years of the schedule are required for finishing the detail of the architectural orders and for surface decoration. Calculating these would be another exercise entirely, but finishing the interior order of the rotunda, and the order and main stonework of the portico, require roughly 25,000 mandays each. For the portico, considerations of the logistics of working suggest that it might have needed two years with a team of some 50–60 marble workers, so that if we also take into consideration the construction and finishing of the internal aedicules as well as the surface decoration, a two- to three-year decorative program seems the most likely.

The relative schedule presented here can be given possible minimum absolute dates. As argued previously, a start date before AD 114 is unlikely, and is consistent with the stamps from the middle and upper zones of the rotunda. If we allow that bricks began to be used very shortly after they were made, the presence of bricks of AD 115 in the middle zone of the rotunda means that it should have been under construction by 116 at the latest, while those of 117 in the grottoni bridge would also work with this schedule. Completion of the decoration would not therefore be possible before 122, and if Lanciani’s report of a fragmentary stamp from behind the decoration of the portico pilasters is correct,40 the finishing and decoration phase may have either continued, or the actual construction been extended, for an extra year or so. The precise dating within these narrow parameters is unrecoverable, and to some extent immaterial for the arguments of this chapter. The key point is that the scheduling suggests the minimum overall time required for completion, and the minimum average number of workers required for that schedule. A longer schedule would only reduce the average number of workers required.

The Pantheon in Context

The results presented here represent only one possible schedule, relating only to part, albeit the main part, of the labor needed for the erection of the Pantheon. To these should be added the work necessary to produce and transport the building materials, which may have increased the workforce by about one-fifth if the Baths of Caracalla are any guide, and all of the small elements such as the exterior brick and travertine cornices that had been omitted for simplification, plus such imponderables as the dome centering. Nevertheless, the figures are remarkably modest for a structure that looms so large in the history of Roman architecture. Even for the suggested nine-year schedule, in most years the minimum workforce engaged in actual construction would not have needed to be more than 240 men, a relatively modest figure compared with a minimum of 4,000 men required for building the central block of the Baths of Caracalla, one of the largest construction projects ever undertaken in Rome, with the possible exception of the aqueducts.41 It should be remembered, for comparison, that the Baths of Trajan, completed perhaps only five to six years before the Pantheon was started, would have required a workforce of similar size to that of the Baths of Caracalla. Even if we increase the workforce for the Pantheon by, say, 20 percent to allow for waste and for men working at less than their full capacity, the numbers are still quite small.

But the Pantheon was not a stand-alone structure (Plate III). In front of it was a porticoed precinct that would have required further manpower for construction, but not necessarily more at any one time, as it must have been built largely after the Pantheon itself was finished, having most likely acted as a works yard for the Pantheon build. The Basilica of Neptune, on the other hand, was constructed at the same time as the Pantheon and physically linked by the grottoni bridge, so that the total numbers of men working at any one time may have been up to a third again as were required for the Pantheon, making a minimum of 300 men in round figures for the two structures. This workforce might then have gone on to work on other buildings in the Campus Martius, particularly the rebuilding of the Saepta and the Baths of Agrippa in the 120s which apparently formed part of the same project of restoration after the fire in AD 110.42 The impact on Rome’s working population could, of course, have been spread wider than this group, as most of the workforce were general laborers and, hence, likely to have been hired only for the short term from a large pool. Nevertheless, the total impact would have been small compared with most of Trajan’s other building projects.

The Pantheon would have had different connotations for Trajan and for Hadrian as part of a fairly extensive restoration project following a major fire. All of the buildings involved were closely associated with Agrippa and thus with Augustus, so that their restoration befitted the emperor who bore the title of optimus and was often spoken of in the same breath as Augustus, following Augustus’s own practice (Res Gestae 20.1) and a long tradition of restoration of public monuments going back into the Republic, with the buildings retaining their original names. Only the completion of the project under Hadrian caused it to be associated with him rather than with Trajan. Hadrian’s own temple building projects, the Temple of Deified Trajan and the Temple of Venus and Roma, arguably would have been far more important for him politically than the Pantheon. The Temple of Deified Trajan, the only one that, according to the sources, Hadrian put his own name on, was a key tool in helping legitimize his succession, and it seems to have used a 60-Roman-foot order, comparable to that of the Temple of Mars Ultor. If we accept Amanda Claridge’s new reconstruction of the temple as hexastyle,43 it would have needed 12 giant gray granite shafts, fewer than the 16 exterior columns of the Pantheon porch, which, as Davies, Hemsoll, and Wilson Jones have argued, were originally designed to be of this size.44 One could therefore suggest that Hadrian, rather than privileging the Pantheon as the epitome of Roman temple construction, commandeered the columns that Trajan had intended for the Pantheon for his own temple to his deified predecessor. The Temple of Venus and Roma made an even greater impact on the topography and political life of the city. The temple was connected with the festival of the Parilia, later known as the Romaia, and is commonly called simply “the temple of the city” in Roman sources.45 Consecrated in AD 121 when the Pantheon was all but complete, and possibly still not finished at the end of Hadrian’s reign, this was the largest temple in Imperial Rome, employing 124 columns 60 Roman feet high, more than ten times the number for the Temple of the Deified Trajan. Moreover, it not only occupied a central position between the Roman Forum and the Flavian Amphitheater but also required the drastic moving of the Colossus of Nero to accommodate it. In plan and height the Temple of Venus and Roma had much in common with the Temple of Olympian Zeus in Athens, which Hadrian is said to have completed, and even features on Rome’s coinage, unlike the Pantheon. Thus, rather than thinking of the Pantheon as Hadrian’s great achievement, we should reserve that accolade for the Temple of Venus and Roma.

Conclusions

These calculations, however hypothetical in some aspects, serve to show that while the Pantheon may have been a triumph of construction, compared with other Trajanic projects including the emperor’s great thermae, or indeed the Temple of Venus and Roma, it was hardly the mammoth undertaking that many have wished to believe. Its Trajanic context reveals it not so much as the signature building of Hadrian the architect, or even of Hadrian the princeps, but as just the last in a series of outstanding and innovative building projects that characterize the reign of his predecessor Trajan.

I am very grateful for the kind assistance of Christina Triantafillou, who worked with me on the basic calculations for the Pantheon, particularly for the grottoni and porch, and provided the key data on the Basilica of Neptune, all of which forms part of her unpublished doctoral thesis for the University of Oxford on the economics of Trajan’s building projects in Rome.

1 Janet DeLaine, “The Romanitas of the Railway Station,” Uses and Abuses of Antiquity, ed. Michael D. Biddniss and Maria Wyke, Bern 1999, p. 150.

2 See most recently Rabun Taylor, Roman Builders, Cambridge 2003, pp. 190–211; Gerd Heene, Baustelle Pantheon: Plannung, Konstruktion, Logistik, Düsseldorf 2004, p. 24; Lynne Lancaster, Concrete Vaulted Construction in Imperial Rome: Innovation in Context, Cambridge 2005, pp. 43–46.

3 Janet DeLaine, “The Baths of Caracalla in Rome: A Study in the Design, Construction, and Economics of Large-Scale Building Projects in Imperial Rome,” Journal of Roman Archaeology, Supplement 25, 1997, pp. 103–109, 174–194.

4 For example, M. E. Blake, Roman Construction in Italy from Nerva through the Antonines, Philadelphia 1973, p. 42.

5 There is in fact no direct dating for the Basilica of Neptune. The 32 brickstamps identified in situ in the grottoni, as listed in Herbert Bloch, “I bolli laterizi e la storia edilizia romana,” Bullettino della Commissione Archeologica Comunale 64, 1937–1938, pp. 108–109, nos. 73–104, have often been erroneously attributed in scholarship to the Basilica (Christian Hülsen, “Thermen des Agrippa,” Römische Gebälke, ed. F. Toebelmann, Heidelberg 1923, p. 67 n. 3; Lanfranco Cordischi, “Basilica Neptuni in Campo Marzio,”Bollettino di Archeologia 5–6, 1990, p. 20 n. 56; Lise Hetland, “Dating the Pantheon,” Journal of Roman Archaeology 20, 2007, pp. 95–112; p. 99). The problem has arisen because of uncertainty in the origins and function of the basilica itself as either an independent structure or an element of the Baths of Agrippa, as well as in the relationship of the grottoni to the two structures. The grottoni brickstamps date to the same time as the Pantheon proper, the late Trajanic to early Hadrianic period. As far as can be seen, no brickstamps can be identified solely and specifically with the Basilica itself. However, unprovenanced brickstamps discovered in the general area of the grottoni and basilica all point toward a contemporaneous date for the two structures (see Bloch 1937–1938, pp. 109–112, for the list of brickstamps).

6 E.g., Luca Beltrami, Il Pantheon: La struttura organica della cupola e del sottostante tamburo, le fondazioni della rotonda, dell’ avancorpo, e del portico, avanzi degli edifici anteriori alle costruzioni adrianee. Relazione delle indagini eseguite dal R. Ministero della Pubblica Istruzione negli anni 1892–93, coi rilievi e disegni dell’ architetto Pier Olinto Armanini, Milan 1898; Giuseppe Cozzo, Ingegneria Romana: maestranze romane; strutture preromane, strutture romane, le costruzioni dell’ anfiteatro flavio, del Pantheon, dell’ emissario del Fucino, Rome 1928, pp. 267–286; Kjeld De Fine Licht, The Rotunda in Rome: A Study of Hadrian’s Pantheon, Copenhagen 1968, pp. 63–78, 94–100, 133–142; Blake 1973, n. 4, pp. 42–48; William L. MacDonald, The Architecture of the Roman Empire, vol. 1: An Introductory Study, London 1965, 2nd ed. rev. New Haven 1982, pp. 94–118.

7 However, in Chapter Five, Gene Waddell argues that once the relieving arches pass into the body of the fabric, they are composed in part of brick, part of concrete. In any case, the overall effect on the manpower figures is relatively small.

8 Licht 1968, pp. 35–58; Louise Rice, “Urbani VIII e il dilemma del portico del Pantheon,” Bollettino d’arte 143, 2008, pp. 93–110.

9 Licht 1968, pp. 48–56, Figs. 52–63, 72; Rice 2008b.

10 According to Licht (1968, p. 44), several of the blocks of the pediment had been used before, and there are Severan brickstamps from the upper part of the intermediate block facade above the portico (Hetland 2007, n. 5, p. 101; for brickstamps: Corpus Inscriptionum Latinarum [CIL], XV 155.2 and 157.1).

11 The exceptional bronze ceiling (or roof) of the caldarium of the Baths of Caracalla makes it clear that the large-scale constructional use of bronze was current in the Severan period; see Janet DeLaine, “The ‘cella solaris’ of the Baths of Caracalla in Rome: A Reappraisal,” Papers of the British School at Rome 62, 1987, pp. 147–156.

12 For roof construction in general, see F. C. Giuliani, L’edilizia nell’antichità, Rome 1990, pp. 59–68. Details are taken from historical sources: the width of the truss elements are assumed to be equal (James Newlands, The Carpenter’s Assistant: The Complete Practical Course in Carpentry and Joinery, London 1990, p. 137), and other dimensions for the various timbers used in traditional systems (e.g., purlin, tie-beam, etc.) are from the tables in C. Paola Scavizzi, Edilizia nei secoli XVII e XVIII a Roma: ricerca per una storia delle tecniche, Rome 1983, pp. 38–42. The number of rafters and battens were determined by the potential size of the (assumed) marble roof tiles. The size of the marble tiles are based on those used on the Pantheon cupola (Lucos Cozza, “Le tegole di marmo del Pantheon,” Città e architettura nella Roma imperiale: atti del seminario del 27 ottobre 1981 nel 25˚ anniversario del Accademia di Danimarca, Odense 1983, pp. 109–118).

13 Beltrami 1898, n. 6, esp. Figs. X–XV, XXII, XXV, XXXIV, and XXXV, summarized in Licht 1968, pp. 172–176; Paola Virgili and Paola Battistelli, “Indagini in piazza della Rotonda e sulla fronte del Pantheon,” Bullettino della Commissione Archeologica Comunale di Roma 100, 1999, pp. 377–394. See also Chapter Two in this volume.

14 Lancaster 2005, n. 2, p. 59, and Fig. 1; DeLaine 1997, n. 3, p. 132, and Fig. 3; Sheila Gibson, Janet DeLaine, and Amanda Claridge, “The Triclinium of the Domus Flavia: A New Reconstruction,” Papers of the British School at Rome 62, 1994, pp. 80–86.

15 See G.T. Schwarz, “Antike Vorschriften für Fundamente und ihre Anwendung auf Römische Bauten in der Schweig,” Provincialia Festschrift Rudolf Laur-Belart, ed. E. Schmid et. al., Basel 1968, pp. 448–453.

16 Note that Licht 1968, p. 92, n. 5, has doubts about the depth of foundations. Even if the clay really does lie under the foundations, then we might expect that it had previously been consolidated by piling, a common Roman technique in water-logged conditions, especially in road construction.

17 Licht 1968, passim, and especially Figs. 97–99, p. 105.

18 Thanks are due to Nikolaos Theocharis and Michael Heinzelmann of the Pantheon project carried out at the Karman Center in Bern for providing figures for the volume of the dome at different levels, thus avoiding otherwise very difficult calculations.

19 For the brickstamps from the Saepta, see Bloch 1937–1938, pp. 107–108; Hetland 2007, n. 5, p. 100.

20 For the importance of such infrastructure in later periods, see Nicoletta Marconi, “The Baroque Roman Building Yard: Technology and Building Machines in the ‘Reverenda Fabbrica’ of St. Peter’s (16th–18th Centuries),” Proceedings of the First International Congress of Construction History 2, ed. Santiago Huerta, Madrid 2003, pp. 1357–1367.

21 The most complete handbook is Giovanni Pegoretti, Manuale practico per l’estimazione dei lavori architettonici stradali, idraulici e di fortificazione per uso degli ingegneri ed architetti, 2 vols., Milan 1869.

22 In London in 1749, ordinary brickwork was rated at 1,000 bricks/day, facework 500/day (B. Langley, The London Prices of Bricklayers’ Materials and Works, London 1749, pp. 87, 100–101). In London in 1865: 700–500 bricks/day (J. T. Hurst, A Handbook of Formulae, Tables, and Memoranda for Architectural Surveyors and Others Engaged in Building, London 1865, pp. 214–216. In Italy in 1869: ordinary brickwork, av. 700 bricks/day (Pegoretti 1869, vol. 2, pp. 144–145). The figures have been adjusted for a common working day of 10 hours.

23 For a discussion of principles and justification of choices made, see DeLaine 1997, n. 3, pp. 103–109.

24 Final figures can thus only be considered as generally reliable to the first significant figure, i.e., the first digit plus the order of magnitude, with the second providing some guidance; thus, for example, a calculated total of 4,237.345 days of labor would be given as 4,240 days to three significant figures, but only the 4,000 would be considered really reliable within the specific assumptions made about working conditions, while the 240 would indicate only that the amount was likely to be closer to 4,000 than 5,000.

25 Licht 1968, pp. 38–39, 62, 87, 157, Fig. 193; cf. Chapter Seven in this volume.

26 See Lancaster 2005, pp. 51–53, on the setting and curing of pozzolanic mortars. Tests on a modern reproduction of Roman concrete using pozzolana from the Bay of Naples show the concrete still gaining strength after a year (E. Gotti, J. P. Oleson, L. Bottalico, C. Brandon, R. Cucitore, R. L. Holdfelder, “A Comparison of the Chemical and Engineering Characteristics of Ancient Roman Hydraulic Concrete with a Modern Reproduction of Vitruvian Hydraulic Concrete,” Archaeometry 50, no. 4, 2008, 576–590).

27 See Chapter Seven in this volume.

28 See Chapter Seven in this volume. While Mark Wilson Jones argues that the impetus for this was a crack in the drum of the rotunda that appeared when the drum was half built, it is also worth noting that the vault that supports the upper part of the grottoni must also have been integral to the Basilica of Neptune, which was less likely to have been able to resist any excess thrust from the Pantheon than vice versa. It is thus possible that the impetus to build the bridge was some structural problem with the Basilica, not with the Pantheon. Note that Licht 1968, p. 148, associates the second buttress behind the Basilica of Neptune apse with the Basilica, not the Pantheon drum. Unfortunately, not enough of the Basilica remains to test this hypothesis.

29 See Chapter Seven in this volume, and cf. Paul Davies, David Hemsoll, and Mark Wilson Jones, “The Pantheon: Triumph of Rome or Triumph of Compromise?” Art History 10, 1987, pp. 133–153; Mark Wilson Jones, Principles of Roman Architecture, New Haven 2000, pp. 199–211.

30 See Rita Volpe and F. M. Rossi, “Nuovi dati sull’esedra sud-ovest delle Terme di Traiano sul Colle Oppio: percorsi, iscrizioni dipinte e tempi di costruzione,” in S. Camporeale, H. Dessales, and A. Pizzo, eds., Arqueología de la Construcción, vol. 3: Los procesos constructivos en el mundo romano: la economía de las obras, Anejos de Archivo Español de Arqueología LXIV, Madrid-Merida, 2012, pp. 69–82.

31 John R. Spencer, Filarete’s Treatise of Architecture, New Haven 1967, IV.23v; Volpe and Rossi 2012, pp. 69–82.

32 This can be calculated as follows, using the lower zone of the rotunda as an example (figures from Table 6.1):Total mandays of bricklayer and assistant laying face, core, and arches/bonding courses = 684 + 40,300 + 240 = 41,224 mandays

Since one-third of this is for the assistants, total mandays of bricklayer working at face = 41,224 x 0.667 = 27,482 mandays

Since maximum number of bricklayers is 104, minimum number of days = 27,482 ÷ 104 = 264.

33 Hetland 2007 and Chapter Three in this volume.

34 Herbert Bloch, I bolli laterizi e la storia edilizia romana. Contributi all’archeologia e alla storia romana (1936–1938), Rome 1947, pp. 103–107.

35 For two different examples, see Herbert Bloch, “The Serapeum of Ostia and the Brick Stamps of 123 AD,” American Journal of Archaeology 63, 1959, pp. 225–240; Janet DeLaine, “Building Activity in Ostia in the Second Century AD,” Acta Instituti Romani Finlandiae 26, 2002, pp. 41–102; pp. 93–99.

36 See Chapter Seven in this volume.

37 Pliny the Elder, Naturalis Historia, 36, 55, records an old prescription in Rome that forbade the use of lime that had been slaked for less than three months.

38 There is evidence to suggest that the area in front of the Mausoleum of Augustus may have been used as a marble working yard for the Pantheon. See Lothar Haselberger, “Ein Giebelriss der Vorhalle des Pantheon. Die Werkrisse vor dem Augustusmausoleum,” Mitteilungen des Deutschen Archäologischen Instituts, Römische Abteilung 101, 1994, pp. 279–308; cf. Martin Maischberger, Marmor in Rom: Anlieferung, Lager- und Werkplätze in der Kaiserzeit, Wiesbaden 1997.

39 See Chapter Seven in this volume.

40 See Bloch 1937–1938, pp. 107, 115, and cf. Chapter Three in this volume.

41 DeLaine 1997, n. 3, pp. 191–193, Tables 21–23. This is just for construction, and just for the central block. Even more men were required for the extensive substructures, as many as 9,000 if these were built in a single year.

42 For the brickstamps of the Saepta dated to 123 and 127, see Bloch 1937–1938, pp. 110–111. For the Baths of Agrippa, see Giuseppina Ghini, “Thermae Agrippae,” in E. M. Steinby, ed., Lexicon Topographicum Urbis Romae, vols. 1–5, Rome 1995–1999; vol. 5, 1999, pp. 40–42. The Scriptores Historiae Augustae (Vita Hadr. xix.10) also lists the Basilica of Neptune, the Saepta, and the Baths of Agrippa alongside the Pantheon among the buildings Hadrian restored at Rome.

43 Amanda Claridge, “Hadrian’s Lost Temple of Trajan,” Journal of Roman Archaeology 20, 2007, 54–94.

44 See note 29.

45 A. Cassatella, “Venus et Roma, Aedes, Templum,” in Steinby 1995–1999, vol. 5, 1999, pp. 121–123.

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