Ancient History & Civilisation

Chapter Seven

“A Zeal for Buildings”: Reshaping of the Space by the Emperors

In late summer, 43 B.C.E., Octavian, then using the self-appointed title of Caesar, rode with his army to the Field of Mars to confront his Senate enemies within the city walls.1 Much had occurred since his first trip to Rome after his adoptive father's assassination. At that time (late May 44 B.C.E.) he had met in the Campus Martius with Mark Antony in gardens that previously belonged to Pompey the Great in order to claim, unsuccessfully, his inheritance.2 Now the young Caesar returned in force. Facing legions camped in the mostly open plain, the Senate wisely yielded to Octavian's demands. Donatives were awarded to his men, and Caesar's heir was made consul, allowing him to enter the city as Rome's sanctioned co-leader. While Octavian was performing sacrifices with respect to his election to consul, twelve vultures were seen, according to Appian and Suetonius, the same number that oversaw the laying of the city's foundation by Romulus.3

Fifty-seven years later, Octavian, now the emperor Augustus, died. His funeral bier was carried on the shoulders of senators through the Campus Martius to be cremated. The space through which the mourners walked was very different from the field that had housed the young Octavian's troops in 43 B.C.E. A series of buildings now rose parallel to the Via Flaminia: the Diribitorium, Saepta Julia, Thermae Agrippae, Stoa of Poseidon, and Pantheon. The arcades of the Aqua Virgo crossed the main road north. Along the western side of the Via Flaminia stood an altar to Augustan Peace, the Ara Pacis, and nearby an imported Egyptian obelisk dedicated to the emperor's triumph over Antony and Cleopatra cast a shadow along a bronze meridian set in travertine. Numerous temples in the area of the Circus Flaminius were rebuilt and rededicated, and two additional permanent theaters were added. The emperor's final resting place, a giant tumulus in a verdant park, waited for his ashes at the far reaches of the Field of Mars. In a span of more than five decades, the Campus Martius was radically altered from a swampy military camp and an infrequently attended memorial to individual valor of republican generals to a thriving and crowded wonderland of communicating architecture for daily sports and recreation and celebrations of the achievements and divinization of the imperial family and the power of the expanding Roman Empire. Later emperors would continue to populate the Field of Mars with extraordinary structures, forever transforming the open, flat plain.


With a clear-eyed focus on his immortality, Octavian constructed his own tomb on the northern edge of the Campus Martius as one of his first building projects (Plan 3, No. 1).4 According to Suetonius, the structure was underway, if not completed, in 28 B.C.E., a year before the young man in his mid-thirties took the title Augustus. By the time the tomb was complete, Octavian had returned from his eastern campaigns and celebrated a grand triple triumph (the same number as Romulus) for his victories over Antony and Cleopatra.5 Placed where the Tiber and the Via Flaminia nearly converge, the structure was viewed easily by both river and land travelers. At a height of forty-four meters and a diameter of approximately eighty-nine meters, the building dominated the northern reaches of the plain in the same way that Pompey's theater overshadowed structures in the central Campus Martius.6

Clearly the siting of the enormous tomb along a heavily trafficked roadway that Augustus would shortly restore was both deliberate and meaningful.7 As the Via Flaminia was often used for military campaign marches to the northern and western regions of the empire, the gigantic mausoleum relayed themes of victory over one's enemies as well as triumph over death through apotheosis. Its accessibility to a major road helped to ensure that visitors to the mausoleum contemplated these messages.8 It was further offset by its immediate surroundings. In accordance with tradition, the mausoleum was placed within a verdant space in which walkways meandered through groves of trees.9 So located, the monument would, in essence, be a signpost to both the Field of Mars and the city. Not only the size and location but also the selection of the architectural design for the tomb likely provided symbolic significance. Possibly influenced by Ptolemaic models, the Mausoleum of Augustus was, according to one author, as much a war trophy as a final resting place.10

Although reconstructions of the now partially preserved circular structure are many and often controversial, Strabo's roughly contemporaneous account illustrates how Augustus's mausoleum rose above the flat plain as another hill of Rome: “The most noteworthy [tomb in the Campus Martius] is what is called the Mausoleum, a great mound near the river on a lofty foundation of white marble, thickly covered with ever-green trees to the very summit.”11 The outermost wall of the round tomb was some twelve meters high and was originally faced on both sides with travertine; what remains today is merely an exposed core of tufa reticulate and mortar construction (Figure 38). Interior concentric walls connected by semicircular buttresses and covered in earth rose above the outer wall, giving the appearance of an earthen mound.12 The thick walls were penetrated by a narrow passageway running from the entrance to a circular, vaulted corridor. The central burial chamber was designed as a circular hall with a pillar in the center. Niches in the walls of the burial chamber and in the central pillar provided space for deposit of imperial remains. A structure for cremation (ustrinum) was constructed nearby.13

At or about the same time that Augustus was focused on his immortal future in the northern Campus Martius, he looked to the past in the southern Campus Martius and refurbished a space that had once reflected the glory of republican military success to one that declared his new power and status. Controlling what Strabo termed the “zeal for buildings” of his “sons and friends and wife and sister,” Augustus undertook to leave his mark on the area around the Circus Flaminius.14 One such “friend” was the general Gaius Sosius, a former partisan of Antony who was arrested after the Battle of Actium but ultimately pardoned by Octavian. Having previously initiated a restoration of the four-centuries-old Temple of Apollo Medicus to honor his own battlefield success, Sosius wisely altered the sculptural program after his reconciliation to depict Octavian's eastern successes and triple triumph in 29 B.C.E. (Figure 39).15 The Temple of Bellona next to the Apollo temple was also rebuilt, possibly under the direction of Appius Claudius Pulcher, an ally of Octavian and a relative of his wife, Livia, and in 33 B.C.E., Octavian's nephew Marcus Claudius Marcellus undertook to rebuild the Porticus Metelli (Plan 3, Inset B). Possibly financed by Octavian, the portico project was dedicated by Marcellus's mother Octavia, Augustus's sister, after Marcellus's death in 23 B.C.E. and named the Porticus Octaviae.16 Octavia also refurbished the temples of Juno Regina and Jupiter Stator and added libraries, and on the northwestern end of the Circus Flaminius, Octavian's stepfather, L. Marcus Philippus, enclosed the Temple of Hercules Musarum in a portico named the Porticus Philippi (Plan 3, Inset B).17 At approximately the same time, Octavian restored the portico just to the west of the Porticus Philippi that had been constructed more than a century earlier by his ancestor Gnaeus Octavius.18 Joining the reconstructed temples and porticoes in the area of the Circus Flaminius were the newly built theaters, one dedicated to the emperor's nephew Marcellus and the other built by a supporter of Augustus, Cornelius Balbus. This clustering of edifices built or reconstructed under the new emperor's effective control created a node of Augustan political display in the southern Campus Martius. Augustus's successors would expand on this theme with an arch to his great-nephew Germanicus, complete with eleven statues of the latter's immediate family, later erected between the Portico of Octavia and the Theater of Marcellus.19

38. South side of the Mausoleum of Augustus. (Photo: Paul Jacobs)

39. Detail, frieze, Temple of Apollo Sosianus (ca. 29 B.C.E.). (Photo: with permission of Roma, Musei Capitolini, Centrale Montemartini)

While the southern campus was the site of mostly refurbishment and rebuilding projects accomplished by Augustus and his allies, the central Field of Mars gained new and extraordinary monuments. These efforts were undertaken by Augustus's most trusted and capable construction overseer, Marcus Agrippa. Agrippa contended with a low-lying, marshy area that was often flooded, a challenge that might have made this location less than appealing had it not been also charged with symbolic capital as the site of the apotheosis of Romulus. Appointed aedile in 33 B.C.E., Agrippa undertook major waterworks in the Campus Martius, including improved drainage systems and water supply channels and construction of the Aqua Virgo.20 He was the first manager of the waters (curator aquarum), a lifetime appointment created by Augustus to address earlier disregard for maintenance of Rome's neglected infrastructure.21 Just north of Pompey's theater complex, he erected in the once swampy area two structures to receive the Virgo's waters, the Thermae Agrippae and the Stagnum Agrippae.22 By combining practical, utilitarian constructions with enhanced areas for leisure and entertainment, Agrippa's program no doubt augmented the popularity of the plain for Roman citizens of all ranks.

Agrippa's baths and Stagnum followed a north-south orientation, in line with the Saepta Julia completed by Agrippa the previous year and the Diribitorium dedicated in 7 B.C.E., five year's after Agrippa's death.23 To the north of his baths, Agrippa also built two additional structures, both of which were damaged or destroyed and substantially reconstructed later in the imperial period: the Pantheon and the building variously identified as the Basilica of Neptune and Stoa of Poseidon.24 The basilica/stoa was constructed between the Baths of Agrippa and Agrippa's Pantheon.25 A large hall on the Via della Palombella, rebuilt by Hadrian, has been identified as originally belonging to this Agrippan building. Like most basilicas, the structure appears to have served primarily a commercial function, further enhancing the practical functions of Agrippa's constructions in the Campus Martius.26 The general details regarding Agrippa's Pantheon, a structure also mentioned in some detail by Cassius Dio, are no less controversial.27 The function of the building, as well as its original shape and orientation, has caused much debate. Although he likely confused aspects of the surviving Hadrianic structure with the earlier Agrippan building, Cassius Dio reported the reasons for its initial construction:

Also, he [Agrippa] completed the building called the Pantheon. It has this name, perhaps because it received among the images which decorated it the statues of many gods, including Mars and Venus; but my own opinion of the name is that, because of its vaulted roof, it resembles the heavens. Agrippa, for his part, wished to place a statue of Augustus there also and to bestow upon him the honor of having the structure named after him; but when the emperor would not accept either honor, he placed in the temple itself a statue of the former Caesar [Julius Caesar] and in the ante-room [porch] statues of Augustus and himself.28

On the basis of Dio's commentary, Agrippa's structure seems to have been planned as a quasi-dynastic structure, linking Augustus not only to his divine father but also to the divine Romulus, whose legendary apotheosis took place near the Caprae Palus.29The shape of Agrippa's lost Pantheon continues to be controversial: some scholars argue for a T-shaped design with a transverse cult space (cella) facing south, while others propose a north-facing structure with a foundation footprint closely resembling the later Hadrianic building, albeit most often without the concrete domed ceiling, an innovative form later celebrated in Hadrian's domed rotunda of the same name.30 In addition to statues of the imperial family and various divinities mentioned in Dio's accounts, Pliny referred to the caryatid sculptures (subjects unknown) by Diogenes of Athens, as well as bronze Corinthian capitals.31 Clearly the structure was adorned with symbols and statues connected with burgeoning Augustan iconography; less clear and more controversial are the design and function of this enigmatic building.

Augustus focused on the northern Campus Martius for the sites of his final two major monuments in the Field of Mars – the horologium and the Ara Pacis Augustae (Altar of Augustan Peace). Following the emperor's return to Rome in 13 B.C.E. after three years of successful campaigns and negotiations in the western provinces (Spain and Gaul), the Roman Senate voted to erect an altar of Augustan Peace. The altar and its enclosure wall were built along the western edge of the Via Flaminia south of the mausoleum (Plan 3, No. 3). While for most monuments in Rome there is a dearth of textual evidence, for the Ara Pacis there survives ample textual evidence, the most prominent of which is a reference in the Res Gestae.32

The Ara Pacis Augustae complex consisted of two main parts: a U-shaped altar proper in the center where sacrifices took place and the walls surrounding the altar, known as the saeptum, that physically demarcated the sacred precinct area.33 Two wide doors allowed entrance from the east (Via Flaminia) and from the west (Campus Martius). The interior surfaces of the marble saeptum walls were carved with imitation wooden slats with pilasters at the corners; suspended garlands of leaves, pinecones, and fruit; the skulls of sacrificed bulls (bucrania); and sacrificial bowls (patera). This decorative scheme might have been an idealized stone version of an archaic Roman wooden templum with dual levels of symbolism: new fertility of the land under Augustus and a return to traditional Roman religious practices and structures. On the exterior, a floral frieze of vines and flowers arranged in a careful, controlled composition with Apollo's swans covered the entire lower zone on all four sides, referencing the new god of the Augustan golden age.34 Four rectangular panels on either side of the doorways in the upper zone carried mythological and allegorical scenes related to the foundation myths of the city: the infants Romulus and Remus suckled by the she-wolf (northwest); Aeneas or Numasacrificing a sow (southwest); the goddess Roma seated on a pile of weapons (northeast); and “Tellus” holding two infants while surrounded by various plants, fruits, and domestic animals (southeast).35 The iconography of these sculpted panels was clear – agricultural prosperity and human fertility would thrive through legitimate warfare and victory under Augustus.36

The final areas of carved decoration were the two processional friezes on the exterior north and south sides of the long saeptum walls. These famous sculptures show heavily draped Romans participating in a supplicatio ceremony, a thanksgiving ritual for the safe return of Augustus (Figure 40).37 Both processions move toward the west and the plain of the Campus Martius. Figures identified in the friezes include Augustus, Agrippa, members of the imperial family, the pontifices (college of priests), the Rex Sacrorum, the quindecemviri sacris faciundis (college of fifteen men in charge of the Sibylline Books) and the septemviri epulonum (the seven men in charge of public feasts), lictors carrying the fasces, and other attendants.38 Finally, the altar proper bore relief sculptures depicting the Vestals, a sacrificial procession, and perhaps images of nations and peoples. Thus, the sculptures that once covered the altar were related to actual events of the dedication ceremonies of the altar performed on January 30, 9 B.C.E., the birthday of Augustus's wife Livia. These rites and rituals were to be repeated annually by magistrates and Vestals for the continuation of peace and prosperity.39

40. Detail, frieze, Ara Pacis. Museum of the Ara Pacis, Rome. (Photo: Album / Art Resource, New York)

Shortly before or after the dedication of the Ara Pacis, Augustus caused to be erected approximately 90 meters southwest of the altar an obelisk of red granite.40 Augustus ordered the sixth-century B.C.E. obelisk shipped from Heliopolis in Egypt to Rome to be incorporated into his plans for the northern Campus Martius (Plan 3, No. 2).41 Measuring just over 21.8 meters high, it is found today, reerected, in the Piazza di Montecitorio about 200 meters south of its original location standing before the Italian Chamber of Deputies (Figure 41).42 An inscription carved on two sides of the base is still visible and notes that Augustus as Pontifex Maximus was dedicating the obelisk to Sol, the sun god, after Egypt was brought under the power of the Roman people.43 According to Pliny the Elder, the needle of Egyptian granite in the northern Campus Martius was surmounted by a gilt ball that allowed a sharp shadow to be cast on a system of bronze markers on the ground.44

41. Horologium gnomon, Piazza di Montecitorio, Rome. (Photo: Paul Jacobs)

Known today as the Horologium Solarium Augusti, the monument has generated significant controversy with respect to its function as well as to its physical and symbolic relationship to the Ara Pacis. Through much of the twentieth century, scholars envisioned the bronze markers as arcuated lines radiating from a central line north of the gnomon generally in the shape of a double ax approximately 150 meters wide.45 Under this configuration, the cast shadow would mark the passage of time, creating, in essence, a sundial.46 Excavations in the area beginning in the late 1970s revealed, however, but one crosshatched bronze line incised in travertine 6.25 meters below street level. The line faced north-south and was within reach of the shadow cast from the original location of the obelisk. Inscriptions in Greek note “Etesian winds stop” and the “beginning of summer” as well as references to the zodiac (Figure 42).47

42. Horologium bronze marker, Via del Campo Marzio No. 48, Rome. (Photo: Paul Jacobs)

The failure to find bronze lines other than the excavated north-south line has resulted in the conclusion by some scholars that the monument functioned solely as a solar meridian to measure noon on each day of the year.48 As a solar meridian was used, in part, to verify the accuracy of the civil calendar with the solar year, the horologium would have held symbolic significance at this time because Augustus was awarded three years earlier the title Pontifex Maximus, a religious position that included responsibility for Rome's calendar.49 In addition to the horologium's connection to Augustus's official duties, arguments have been advanced for a functional relationship between the meridian and the monument to Augustan peace. It has been proposed that on the fall equinox, the date of Augustus's official birthday (September 23), the shadow cast by the gnomon's ball follows a line perpendicular to the meridian and points to the entrance of the Ara Pacis. This claim has drawn considerable scholarly criticism, as well.50 While the theory of the gnomon's shadow on the fall equinox has drawn fire, it appears that the three major Augustan monuments in the northern Campus Martius were configured in a manner that would have provided a clear visual interrelationship.51 Because the Ara Pacis and the horologium were constructed so closely in time and space, there can be little doubt that their relationship with the mausoleum to the north was an intentional manifestation of Augustan power. Late in the principate the red granite shaft from Heliopolis harkened back to the defeat of Egypt and the beginning of an era of peace, resonating with the nearby mausoleum that was built when the defeat was fresh and peace still not guaranteed after a long civil war. The horologium, in combination with the nearby Ara Pacis, expressed and augmented Augustan concepts: the cyclical nature of time, the return of the golden age, and the significance of contemporary astrology for the maintenance of the order and the wealth and fertility brought by Augustus's providential rule. With the large circular mound of the mausoleum within sight to the north, the entire northern Campus Martius, previously devoid of any significant structures, became laden with a complex series of intertwined messages of imperial power, divine consent, and immortality through apotheosis.

With the completion of the horologium and Ara Pacis, more than thirty-two structures in the Campus Martius had been newly constructed or refurbished under the emperor's watchful eye. Augustus treated the northern flatland as a tabula rasa on which to imprint monumental symbols of imperial power.52 At the same time he reorganized the space physically, the emperor altered the campus administratively. In 7 B.C.E., the Field of Mars was officially “incorporated” into the bureaucratic control of the capital as one of the fourteen districts (Urbs XIV Regionum) under a plan that was innovative and without republican precedent. Seven of these newly created regions, including the Campus Martius, lay outside the traditional boundaries of the pomerium, although the restrictions imposed on those entering the city had been modified with respect to the emperor. For instance, in 23 B.C.E. Augustus was authorized to utilize tribunal powers, normally reserved for the city limits, within a mile of the pomerial line, an area that would include the Campus Martius. Additionally, from 19 B.C.E. Augustus, and then later emperors, had consular imperium, a status that allowed them to command troops and to appear in military uniform within the city.53 Not only the physical but now also the religious lines between the city proper and the Campus Martius were becoming blurred.

Following Augustus's death in 14 C.E., two matching pillars were erected outside the entrance to his mausoleum.54 They were adorned with bronze tablets inscribed with the Res Gestae, a document composed by the princeps himself that detailed his political, military, architectural, and civic achievements. He noted with pride certain of his projects in the Campus Martius – the Ara Pacis, the Porticus Octaviae, the Theater of Marcellus, and reconstruction of the Theater of Pompey and the Via Flaminia.55 At the top of the tomb's exterior, a statue of the emperor, likely a colossal gilded portrait, was held aloft by the central pillar – the same pillar that housed the cremated remains of members of Augustus's family and perhaps the emperor's funerary urn.56 The elevated position of this portrait statue, rising above the tomb and the plain of the northern Campus Martius, no doubt celebrated and reinforced the apotheosis of the princeps. Just as Romulus had once risen to the heavens from the Field of Mars to join the Roman pantheon of gods, so too did Augustus.57


Other than the imperial bath complex commissioned by Nero discussed previously (Thermae Neronianae), little major building or restoration activity altered the general topography of the Campus Martius during the era of the Julio-Claudians (r. 14–68 C.E.). Claudius, however, extended the pomerium into the central plain, an act that brought an area dedicated to the military within the city limits for the first time.58 Likewise, Vespasian (r. 69–79 C.E.) and Titus (r. 79–81 C.E.), the first two rulers of the Flavian Dynasty,concentrated their construction efforts elsewhere. The destructive conflagration of 80, however, ravaged large portions of the Field of Mars and likely encouraged the prolific architectural patron, Domitian (r. 81–96 C.E.), to undertake costly repairs as well as the financing of new construction.59 Structures listed as destroyed or damaged include but were certainly not limited to the temples of Isis (Iseum Campense) and Serapis (Serapeum), the Saepta and Diribitorium, the Basilica of Neptune and the Baths of Agrippa, Agrippa's Pantheon, the theaters of Balbus and Pompey, and the Porticus Octaviae. As becomes clear, Domitian's interests in the Campus Martius did not continue the major trends begun by Augustus. Rather than emphasizing universal triumph and imperial apotheosis, Domitian built and repaired structures that were far more personal in nature. Nevertheless, Domitian's constructions permanently reconfigured and further enhanced the activities and rituals that took place on the plain.

The Serapeum and Iseum Campense (occasionally referred to as the Temple of Isis Campensis) were originally built as early as the late republic. They stood within the same precinct and represented the official cult center for Isis and Serapis in Rome.60 It is not surprising that Domitian took particular interest in rebuilding their shrines; ample evidence demonstrates his fascination with Ptolemaic Egyptian religion and with Isis in particular.61 What we know of the design of this temple complex comes from the remaining fragments of the Severan Marble Plan as well as from a late first century C.E. relief from the tomb of the Haterii, a family of builders, that possibly shows a small, triple arcade from the precinct area, the “Arco di Camigliano” (Figure 43).62 Located between the Saepta and the Via Flaminia, much of the details of the plan of the Iseum are gone and therefore difficult to reconstruct. The Serapeum, better preserved on the Marble Plan, appears to have been a large rectangular courtyard connected on its western side by means of a grand portal to the Saepta Julia. A portico with four apsidal exedras projected from a portico shaped like an inverted D south of the courtyard (Plan 4, Nos. 6 and 7).63

43. Detail, tomb of the Haterii, depicting “Arcus ad Isis” (so-called Arco di Camigliano?) (late first century C.E.). Museo Gregoriano Profano, Vatican Museums. (Photo: Scala / Art Resource, New York)

While we have only a few tantalizing hints as to the architecture of this Egyptian complex, a surprisingly large quantity of artwork that decorated the precinct has survived. Statues of water gods (Nile, Tiber, and Oceanus; see Figures 36 and 37) as well as a basalt sculpture of a baboon survive, as do several obelisks (Obelisci Isei Campensis), including those currently located at the Piazza Santa Maria sopra Minerva (Figure 44), the Viale delle Terme Diocletiane, and the famous obelisk decorating the ornate fountain in the Piazza della Rotunda (Plate I). Another Egyptian obelisk that may have once stood inside the Iseum precinct, the Pamphili Obelisk, is carved with unusual hieroglyphs and images that celebrate Domitian as both the emperor of Rome and the pharaoh of Egypt.64A large marble foot from an acrolith and known as the Pie’ di Marmo rests on a pedestal outside in the area where the complex once stood (Figure 45).

44. Obelisk from Iseum incorporated in Bernini's Elephant and Obelisk, Piazza Santa Maria sopra Minerva, Rome. (Photo: Paul Jacobs)

45. Marble foot from an acrolith (so-called Pie’ di Marmo), Via di Pie’ di Marmo, Rome. (Photo: Paul Jacobs)

Just to the east of the temples of Isis and Serapis is a second set of structures associated with Domitian's rebuilding program in the Campus Martius following the fire of 80 C.E. Again, the character of these constructions represents a departure from Augustus's program and is closely tied to the personal and dynastic interests of the last Flavian emperor. A possible replacement for the remaining space in the much diminished Villa Publica and similar in general design to the Forum Pacis, the Divorum consisted of a large, open quadriporticus within which stood two temples, one dedicated to Divus Vespasianus and one to Divus Titus, and possibly the (repaired?) altar to Mars (Plan 4, No. 9).65 To the north of the Divorum and east of the Temple of Isis and Serapis was another precinct that once contained a round temple (tholos) of Minerva Chalcidica (Plan 4, No. 8). It serves as yet another example of Domitian's devotion to the warlike goddess Minerva, for whom he built temples and shrines throughout the city and with whose image he decorated multiple issues of his coinage as well as state reliefs.66

In addition to this concentration of religious structures east of the Saepta, Domitian constructed new entertainment facilities west of the Baths of Agrippa and Nero, in keeping with the uses established in the central Campus Martius over the previous century. Used for contests and spectacles, these structures were known as the Stadium of Domitian and the Odeum of Domitian (Plan 4, Nos. 19 and 20). The second structure, the Odeum of Domitian, has disappeared; although scholars have a general sense of its location south of the stadium, its overall shape (rectangular vs. semicircular) remains controversial. Both of these projects can be connected with Domitian's philhellenism and his reintroduction of Greek-style contests known as the Capitoline Games in honor of Jupiter. Like Minerva, Jupiter was a favorite deity of Domitian, and these constructions in the central area of the plain are testament to his attempts to promote Greek agonistic festivals as well as his personal interest in Greek literature, culture, and sport. With the completion of Domitian's stadium and odeum, we see a pattern of building distribution emerging in the imperial period: religious precincts added to the eastern side of the central zone, new leisure and entertainment facilities constructed to the west. The last vestige of an open space in that part of the field that had witnessed for centuries so many popular gatherings outside of the pomerium, namely the Villa Publica, was now enclosed within a regularized portico structure. Meanwhile, the northern campus (physically separated from the central field by an east-west road) still remained a vast and open “Augustan park,” with grand buildings and ornately decorated monuments that celebrated the more abstract concepts of perpetual triumph and imperial apotheosis.

Hadrian and the Antonines

Following the assassination of Domitian in 96 C.E., the emperors Nerva and Trajan undertook projects that consisted of either completing or restoring earlier Domitianic construction (Forum Transitorium, Forum of Julius Caesar) or initiating new projects (Forum of Trajan, Baths of Trajan). However, during the years 98–117, little significant attention was paid to constructions or restorations in the Campus Martius. Renewed activity on the plain took place in earnest, however, during the early years of the reign of Hadrian. TheHistoria Augusta provides a brief description of Hadrian's building projects in the capital: “At Rome he restored the Pantheon [Pantheum], the Voting-enclosure [Saepta], the Basilica of Neptune, very many temples, the Forum of Augustus, the Baths of Agrippa, and dedicated all of them in the names of their original builders.”67

Hadrian spent ample resources in the central Campus to restore earlier structures and, like much of his program, his interests focused on projects associated with Augustus and the Julian gens. His work on the Augustan Saepta appears to have involved a reconstruction of the west portico of the building, including an access route between the northwest corner of the Saepta portico and the facade of the Pantheon.68 Also associated with Hadrian's constructions in this area is the large hall located south of the Pantheon and most often associated with the Agrippan Basilica of Neptune.69 Hadrian's restoration of the Baths of Agrippa should also be seen as part of this overall program of renewal and refurbishment of structures associated with Augustus and Agrippa in the central zone of the Campus Martius.

One of the best-preserved ancient structures in Rome is also one of the most enigmatic – Hadrian's Pantheon (Plan 4, No. 14).70 Like Agrippa's earlier structure on whose site it rests, Hadrian's Pantheon is the object of intense scholarly discourse as to its function and meaning. Unlike the Augustan era structure, the Hadrianic building at least has an observable architecture, but after centuries of alterations, questions about dating and form still remain (Plate I).71 The structure comprises three primary elements: the porch, an intermediate block, and a drum or rotunda. Originally, the Pantheon was set atop a podium with five marble steps leading to the pronaos, but the rise in the level of the ground around the building has buried this area to the level of the porch paving. Thepronaos bears a total of sixteen columns with monolithic shafts of Egyptian granite, with eight gray granite columns across the facade (octostyle). Four rows of two red granite columns each are arranged to divide the porch area into three distinct aisles. All of the columns display entasis (subtle diminution of diameter as they rise) and all bear Corinthian capitals and bases of white marble. The columns are 40 Roman feet (11.8 meters) high, which is large but not uncommon in ancient Roman construction.72 The wider central aisle leads to the main doorway, while the side aisles terminate in large niches that possibly held statues of Augustus and Agrippa, perhaps preserved from the earlier structure.73 All of the porch columns carry entablatures, which over the two inner rows of columns support piers and arches. This system, together with the exterior columns and their entablatures, once bore a bronze roof structure removed in the seventeenth century. Today, the tiled roof is supported by wooden framing that is visible from below, although in Hadrian's day it was likely covered by an imitation barrel vault.74 The restored porch pavement consists of dark granite and white marble forming patterns of oblongs, squares, and circles. The pediment of the porch (which is now blank) reveals attachment holes, some ancient, indicating that decorative elements were applied to the space. It has been conjectured that a bronze eagle within a wreath graced the center.75 Bronze letters, although not original, do remain in place on the architrave proclaiming: M AGRIPPA L F COS TERTIVM FECIT (Marcus Agrippa, the son of Lucius, three times consul, built this). While Agrippa was given credit in the inscription for the construction, Augustus's friend and builder of the original Pantheon was long dead when this structure was erected.76 One ancient source states that it was the emperor's modesty that caused him to proclaim Agrippa as the builder.77

Tying the rectangular porch to the cylindrical central structure is a transitional block that is the same width as the porch but the same height as the rotunda. Like the domed rotunda behind, the rectangular connector was constructed almost entirely out of brick and mortar. The transitional block has two side chambers that extend all the way up to the top of the structure with staircases leading to several vaulted chambers. One of the oddities of the relationship of the porch to the intermediate block is that the latter is as high as the top of the drum behind it, while the pronaos is not, resulting in “two stacked, interfering pediments of the pronaos and transitional block” (Figure 46).78 The differential would have been solved if the builders had used columns for the porch that were fifty Roman feet in height instead of forty, and it has been proposed that the resulting configuration was the product of an architectural compromise when the larger shafts could not be obtained to meet the construction schedule.79

46. Detail, Pantheon porch and transitional block. (Photo: Paul Jacobs)

Behind the intermediate block is the domed rotunda that is nearly twice as high and two-thirds as wide as the pedimental porch. The interior volume is contained within an almost perfect sphere measuring 147 Roman feet (43.5 meters) from the floor to the ceiling, as the hemispherical dome is as tall as the drum on which it rests.80 The dome itself, made of solid concrete fashioned from pumice, a relatively light volcanic stone aggregate, was poured over a huge wooden form shaped like the resulting hemisphere and supported by wooden scaffolds.81 Each coffer likely contained a gilded rosette in the center and a molding around its edge.82 At the top of the dome, an opening (oculus) 30 Roman feet (8.9 meters) in diameter and edged in gilded bronze allowed in natural light as well as the elements.83 It continues to do so today (Figure 47).

47. Pantheon interior. (Photo: Paul Jacobs)

There are two stories beneath the vast expanse of the dome. The first story consists of eight large recessed bays between eight hidden piers. Six of the bays are screened by two columns each. Between the niches and in front of each pier is a tabernacle oraediculeon a raised podium. The space is faced in various colored marbles from throughout the empire. As William MacDonald has noted, “The result is a scenic, theatre-like wall, richly worked with light and shade, cornerless and continuous.”84 The second story, substantially modified in the eighteenth century, contained a pattern of alternating blind windows and pilasters over a band of marble.85 The floor was decorated with thin slabs of colored stones (granites, marbles, and porphyry) arranged in a large geometric pattern much like a checkerboard.86

Efforts have been made over the centuries to find intentional symbolism in the interior's geometry. Writing decades after Hadrian's death, Cassius Dio thought the dome “resembles the heavens,” but more recently it has been argued that the design of the Pantheon interior was an expression of Hadrianic intellectual and sensual interest in arithmetic ideals and geometry, with the arrangement of the coffers in 28 vertical lines, creating a deliberate visual manifestation of the second perfect number (28 equals the sum of itsdivisors, excluding itself: 1+2+4+7+14=28).87 The obvious play of sunlight through the oculus has not gone unnoticed. At local noon on April 21, the sun's rays entering the oculus strike the north-facing door. This occurrence on Rome's birthday in a building sited in the area of Romulus's apotheosis and on the same day that the sunrise is in line with the east entrance to the Ara Pacis raises huge possibilities for intentional imperial symbolism.88

The Pantheon we see today was completed early in Hadrian's reign, likely sometime in the period 125–28 C.E.89 It has been generally accepted that the project began in 118/19 C.E.90 Approximately the same height as Augustus's mausoleum, the Pantheon's dome could be appreciated at a distance, but the drum was mostly hidden by surrounding structures.91 A forecourt framed by a colonnade extended some 100 to 150 meters north, and visitors would reach the pronaos through either lateral stairs or the flanking colonnade.92 The fact that the exterior design was well hidden must have made the interior that much more surprising and extraordinary to those allowed entrance. While its name in Greek, Pantheon (Pantheum in Latin), technically referred to a temple dedicated to all the gods, there is disagreement whether this label was a nickname or an official designation.93 Cassius Dio recorded that sometime after 125 C.E., Hadrian used the space as an imperial audience hall, reading proclamations from a tribunal upon his return to the capital following one of his tours of the empire.94

In addition to his construction of the Pantheon, Hadrian commissioned a precinct in the central Campus Martius for the worship of his deified mother-in-law, Matidia (Plan 4, No. 13). The complex, which may have also included basilicas dedicated to Matidia and Marciana, appears to have been a large peripteral temple surrounded by deep porticoes, the columns of which may have been constructed from different-colored imported granite.95 Taken together, the Pantheon and the nearby Diva Matidia complex offer additional support for the hypothesis that Hadrian deliberately refurbished Augustan structures and constructed new dynastic buildings to celebrate his family and their connections with the glorious past of Augustan Rome. No district of the capital was more suited for such a building program than the central Campus Martius.96

Following Hadrian's death in 138 C.E., work commenced on a temple in the central Campus Martius just east of the Temple of Matidia. It was dedicated to the Divine Hadrian (Divus Hadrianus) in 145 C.E. by his successor Antoninus Pius (r. 138–61) (Plan 4, No. 4).97 Eleven of the original thirteen fluted, Proconnesian marble columns of the northern flank of the peristyle can be seen on the northern side of the Palazzo della Borsa (former Roman Stock Exchange) in Piazza di Pietra (Figure 48).98 Originally, the temple had a frontal staircase on the east, all raised on a podium made of peperino tufa and faced with marble. The cella was roofed by a coffered barrel vault (similar to the coffered vestibule of the intermediate block of the Pantheon), a section of which is still preserved inside the former Borsa. The interior was accentuated by engaged columns.99 In the area around the temple, twenty-four marble panels and pedestals have been discovered that have been associated with the temple or an enclosing portico.100 They display reliefs of allegorical figures believed to represent the Roman provinces alternating with reliefs of weapons and trophies (Figure 49). The entablature of the interior cella colonnade had a frieze of spiraling acanthus candelabras possibly presenting a deliberate association with common Augustan decorative iconography.101

48. Temple of Divine Hadrian, Piazza di Pietra, Rome. (Photo: Paul Jacobs)

49. Marble panels from the area of the Temple of Divine Hadrian, Musei Capitolini. (Photo: Scala / Art Resource, New York)

Following the death of Antoninus Pius, an unfluted, red granite column was raised to his memory and that of his wife Faustina in the northern Campus Martius southwest of Augustus's horologium complex.102 Approximately 14.75 meters high, the shaft sat on a white marble base, now in the Vatican (Figure 50).103 In keeping with the imperial theme of apotheosis with which the Campus Martius had become associated, the base displayed a relief of Antoninus Pius and his wife lifted to heaven on the wings of a figure thought to be Aion, a god of eternity. An eagle above each of the god's wings symbolized the spirits of the divine couple ascending to the heavens. To the lower right is the goddess Roma, seated and surrounded by weapons; to the left is a reclining seminude personification of the Campus Martius holding an obelisk with an orb, likely the obelisk that served as the gnomon for the Horologium Augusti.104 Flanking reliefs on the base show funeral rites (decursio) performed prior to lighting the pyre. Given the types and locations of funerary monuments in this zone of the central Campus Martius, one scholar has labeled this area of the plain as an Antonine “apotheosis landscape.”105

50. Column of Antoninus Pius, base relief (ca. 161 B.C.E.). Apotheosis of Antoninus Pius and his wife Faustina. Vatican Museum. (Photo: Album / Art Resource, New York)

While the base of the Antoninus Pius column and nearby commemorative funerary altars reminded Romans that its greatest leaders left for heaven from the Field of Mars, another nearby Antonine monument reflected the space's military themes. In honor of the defeat of the Sarmatians and the Marcomanni in 172–75 C.E. by the emperor Marcus Aurelius (r. 161–80), the Senate commissioned a large column to be erected just west of the Via Flaminia in the northern Campus Martius (Figure 51).106 Comprising twenty-six drums of Luna marble with an internal spiral staircase of 200 steps, the monument on its base rises 100 Roman feet (29.77 meters).107 Clearly based on the design of the earlier column of Trajan in the Forum of Trajan, scenes of the two campaigns of Marcus Aurelius are deeply carved into the marble and are separated by a personification of Victoria. The depictions of violence are graphic, including the beheading of barbarian men and the brutal capture of provincial women and children. Most famous is the “Miracle of the Rain” scene, which depicts a bearded god with outstretched arms dispensing a torrential storm to aid the entrenched Roman legions (Figure 52). The position of the column and its decorated pedestal base on the Via Flaminia was deliberate and purposeful. The most important scenes in the helical reliefs (Victory, Rain Miracle, Crossing the Danube) as well as the pedestal entrance doorway to the internal spiral staircase were easily seen from the roadway.108

51. Column of Marcus Aurelius, Piazza Colonna, Rome. (Photo: Paul Jacobs)

52. Detail, Column of Marcus Aurelius, “Miracle of the Rain,” Piazza Colonna, Rome. (Photo: Paul Jacobs)

The Severans and Late Antiquity

As was the case with the first two Flavian emperors, as well as Nerva and Trajan, the Severans did not commit many resources to constructions in the already crowded central and southern zones of the Campus Martius. Their interests in commissioning new structures were focused on other regions of the capital, and Severan restorations of structures on the plain are limited, such as poorly understood minor repairs of the Hadrianic Pantheon.109 This early third-century restoration of the Pantheon was a minuscule manifestation of the much broader program of Septimius Severus to connect his dynasty with areas of and structures in Rome associated with the Divine Augustus.110 The last emperor of the Severan dynasty, Alexander Severus (r. 222–35), rebuilt and enlarged the earlier Baths of Nero in 227 C.E. as discussed in Chapter 6.

The next major architectural changes to the Campus would not be realized until the reign of Aurelian (r. 270–5 C.E.). Construction of an 11-kilometer-long, 6.5-meter-high brick wall, fortified with defensive turrets at regular intervals, was begun sometime before Aurelian's wars against Zenobia in 271–2 C.E. Work on the massive structure continued for another ten years; it was finally dedicated by Aurelian's successor, Probus (r. 276–82 C.E.), while extensive restorations and additions continued in the fourth and early fifth centuries.111 The erection of Aurelian's Wall marks the first time that the fortified physical boundary of the city incorporated the Campus Martius, as previously the so-called Servian Wall had not included the plain within its much smaller perimeter. Following Aurelian's defensive construction, the Campus was integrated once and for all within the official, imperial-sanctioned boundary of the capital city.

Spaces Between the Monuments

Over three centuries, the emperors left their deep imprint on the Field of Mars, filling most of the plain with baths, temples, porticoes, and theaters. There remained, however, room in the interstices among the grand structures in which to squeeze residential and commercial establishments. This helped assure that the Campus Martius would function as a living space as well as a destination for entertainment and relaxation. As early as the first century B.C.E., public land in the plain was sold to raise money for the treasury, and Caesar planned to enlarge the Campus Martius and create living space for an increasingly crowded city.112 His scheme was not realized, of course, and apart from several notable villas, housing in the Field of Mars was kept in check by the large areas devoted to massive public buildings and parks. Nevertheless, as the great monuments were erected in the imperial era, residents also moved in. By the fourth century C.E., the northern plain reportedly contained almost 2,800 insulae, approximately 6 percent of all such units in the city at the time, and 140 or almost 8 percent of the city's private homes.113 Although these numbers appear impressive, given the size of the Campus Martius, the density of insulae there has been calculated to be the lowest of the fourteen regions and the density of domus near the lowest, reflecting the large area occupied by public buildings.114 Glimpses of some of these buildings can still be found under the modern city. Beneath a cinema just east of the Corso and close by the Trevi Fountain are the remains of a three- or four-story apartment building constructed following the great fire of 64 C.E. In the fourth century, the structure was converted to a luxurious home.115 Northwest of the Circus Flaminius, a horrea dating to the late first century C.E. was converted in the late second to early third century C.E. to an insula. Portions of the structure are still visible under a palazzo on the Via di S. Paolo alla Regola.116 Just north of the Stadium of Domitian and beneath the Renaissance Palazzo Altemps, now a museum, can be found walls from a reception room of a grand first-century C.E. domus.117

In the northern Campus Martius near the horologium and Ara Pacis, beautiful homes began to occupy the still-open spaces in the late second century C.E., only to be replaced by large insulae in the third century. Parallel to the Via Lata and just north of the Ara Pacis, a large insula was constructed. At least two stories in height, it contained commercial establishments or businesses for small industry on the ground floor. The remains beneath the Church of San Lorenzo in Lucina disclose a row of nine rooms running north and south with a staircase. Brick stamps date the construction to the time of Caracalla (r. 198–217 C.E.), and the building was in use until the early church basilica was constructed in the fourth century C.E.118 Evidence of another large second-centuryC.E.structure, possibly an insula, has been found just north of the Church of San Lorenzo in Lucina.119 The deliberately triangulated space created by Augustus two centuries earlier to express the glories of his reign was now giving way to pedestrian structures that reflected a Campus Martius for the masses.


With the concentration of state power in the hands of the emperors, the Campus Martius converted from a mostly open and occasionally visited marshland to an integral part of the city, imbued with symbols of its past and altered to accommodate the exigencies of the expanding urban space. Development under Augustus was no longer small scale and piecemeal, as the wealth and political will of the principate could be brought to bear, transforming large spaces within decades rather than centuries. Where republican military might had been accommodated seasonally in a flat, open topography of swamp and grasses, imperial strength became reflected daily in a landscape of organized, marbled edifices stretching skyward. What had been the area for war, tribal elections, and celebrations of individual accomplishments during the republic became the people's marble park, a crowded but salubrious space where inhabitants could stroll, play, negotiate, and live in the shade of imperial cult temples and permanent stone memorials. Grandiose imperial spaces enveloped the small nodes of republican development. Drainage channels and aqueducts allowed imperial style bathhouses and artificial lakes to replace ponds. Whereas some emperors such as Nero and Domitian focused their resources on building public entertainment and leisure facilities, others followed Augustus's lead and commissioned magnificent temples and funerary monuments designed to declare and perpetuate the ideologies of imperial apotheosis and dynastic continuity. In the field that saw the ascension of Romulus, where Rome's first king dissipated in a mist, later emperors created monuments to ensure the permanent record of their own apotheoses. The imperial structures were designed to attract visitors and, in turn, created the conditions for residential and commercial development in the spaces between the monuments. The zeal for building had overtaken the grassy spaces of Strabo where one could exercise without hindrance, and after three centuries the Field of Mars endured, but fully urbanized, converted and transformed in use and import, subsumed by its “mere accessory.”

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