This story of portraiture has shown a combination of influences deriving from many parts of the Greco-Roman world. During the whole of the period the provinces had been gaining in importance at the expense of Italy; while Rome itself, even more heavily subsidised than the rest of the peninsula (p. 52), had become–in all but its immense monuments and no less immense prestige – no more than one among a number of capitals.
This transformation is clearly mirrored in the development of the imperial mints which provided coinage for the army and the empire. In the second century AD, with the exception of issues at Alexandria and certain other cities striking Greek denominations, the official currency, even if partly (for convenience’s sake) coined in the provinces, depended upon the Roman mint for its central administration, design and style. But from the time of the civil wars of 193–7 it becomes possible to detect the operations and distinct designs of separate official mints for gold and silver money in various parts of the empire.43 As the third century proceeded, fresh mints for gold and base metal sprang up temporarily as generals grasped at the purple. Moreover, the central emperors, too, now used widely dispersed official mints which become more and more clearly distinguishable, and sometimes identifiable with a particular town.44 Then, from the reign of Gallienus and increasingly under Aurelian, imperial coins begin to bear mint-marks explicitly indicating the city of their origin.45 These appear regularly on the vast, homogeneous coinages of Diocletian and his colleagues, whose centralisation of control could only be effectively undertaken by decentralising manufacture.46
By that time, it was nothing new for emperors to find Rome inconvenient as a base for their government, which was so largely based on military needs. Many rulers had spent years near the northern and eastern frontiers. For example, Sirmium (Sremska Mitrovica), the most important strategic centre in the Danubian area, became for considerable periods the headquarters of Marcus Aurelius, Maximinus I and other emperors. When Valerian found it necessary to divide the government of the empire with his son Gallienus, Antioch became a duplicate imperial capital; and after Valerian was dead, military threats to northern Italy made Gallienus treat Mediolanum rather than Rome as his residence.
When Diocletian and Maximian again divided the empire between east and west, they were assisted by two Caesars, so that there were now four capitals. In the west, Maximian lived at Mediolanum and his Caesar, Constantius I Chlorus, at Augusta Trevirorum (Trier). In the east, the second Caesar Galerius dwelt at Thessalonica (Salonica), a strategic rear headquarters to Sirmium and the vital Danube command. But the senior capital was the place where Diocletian had been nominated to the throne and where he also chose to reside, Nicomedia on the Sea of Marmora. Nicomedia possessed a good harbour (the Turkish naval port of Izmit today), and was strategically situated out of danger of invasion but on the main line of communication between the Danube provinces and the eastern frontier (Danube–Morava – Maritza – Asia Minor – Antioch – Euphrates). This was the sort of consideration which now weighed heavily in the choice of a capital, and Constantine, after living at Augusta Trevirorum (Trier), Arelate (Arles) and Ticinum (Pavia), settled successively at two important cities of his native Balkans which were situated on the main strategic route, first Sirmium (c. 317) and then Serdica (Sofia). ‘Serdica’, he said, ‘is my Rome’.47
But the necessities of imperial defence would best be served by a headquarters situated at the point where the road between Danube and Euphrates is crossed by the maritime passage linking the Mediterranean and the Black Sea. The two lines meet in the narrows at the Hellespont (Dardanelles) and the Bosphorus. Near the former point, Constantine was reported to have begun building at Troy.48 But he preferred the Bosphorus, and rebuilt its ancient city of Byzantium as Constantinople (324–30). This site, near to which his fleet had just won a decisive victory over Licinius, possessed the majestic harbour of the Golden Horn. The place was also fortifiable by land and sea (as it had shown in a long resistance to Septimius Severus) and possessed easy accessibility, again by land and sea alike, to the all-important industrial and cultural centres of Asia Minor and Syria, and to the corn of Egypt which was needed to maintain a large population.49 Byzantium, it is true, had no Christian tradition; moreover, the initial foundation rites of Constantine’s city were pagan and the Sun-god played a central part in them (p. 181). Nevertheless, the new foundation could be bent to the imperial will and made Christian with greater ease than incurably pagan Rome (p. 239). Constantine may not have announced immediately that the new city he had created was to become his sole imperial residence, or that it should be called the New or Second Rome.50 However, like its antique model, it was given a forum and a senate of its own, and its population received free distributions from the cornfleet which had previously served the more ancient capital. In c. 330 there were special coinages honouring CONSTANTINOPOLIS; but they were paralleled by issues celebrating the City of Rome. For the emperor was proceeding carefully. Rome lost none of its privileges, and at first Constantinople ranked as its inferior, with its senators taking a lower precedence than those of the ancient capital. Nevertheless, it was Constantine’s intention to make Constantinople his single headquarters.
And so the scene was set for the Middle Ages. The western empire went under, but the eastern Byzantine empire survived because of its lesser vulnerability, bigger population, more efficient government, and larger and more equitably distributed economic resources. Constantinople was not only the capital of that empire but, until its capture by the Latins (1204–61), the most important place in Europe, the representative of the Mediterranean great city in a new age. Then, after nearly two more centuries of Byzantine rule, it again achieved extraordinary magnificence and prosperity when the Ottoman Turks made it their capital (1453). By the sixteenth century, Istanbul was once more the centre of an empire without equal in the west. The city founded by Constantine has rivalled Rome as a political, spiritual and artistic leader of the world.
In spite of almost perpetual financial crisis, imperial prestige required that imperial buildings should be bestowed upon these cities with unprecedented lavishness. At Rome, in particular, despite its waning political and economic significance, public buildings occupied a far greater proportion of space than in any modern city, and their creation and adornment formed an important part of official policy. The Severan dynasty was the last to change the face of Rome extensively. Septimius constructed a fanciful magic castle of fountains on the Palatine Hill, the Septizodium (203). His own statue appeared as the Sun-god, whose role in official paganism was growing (p. 176). It stood among the Seven Planets of astrology, which had also figured prominently in the Pantheon constructed at Rome by Augustus and refounded by Hadrian. But whereas that had been the most splendid hitherto of all domed designs, the Septizodium stood for the more antique tradition of verticals and horizontals. Although it was finally demolished in 1588–9, its elegant cumulation of three tiers of porticoes, one upon another, is to be seen from Renaissance illustrations.51 The style is reminiscent of similar buildings, perhaps of Asian inspiration, in Septimius’ north African homeland,52 and the ornamental facade of the Septizodium was orientated not towards the forum but to the emperor’s fellow-Africans arriving at Rome by the Sacred Way.53
The orthodox Greek rectangular temple, which had been magnified by the Romans to novel dimensions, attained spectacular elaboration and size in the centre of Sun-worship at Heliopolis (Baalbek, Lebanon). There, upon the artificial vaulted terrace of the Sanctuary with its superb religious adaptation of forum-like axial planning, a huge shrine of Jupiter and the Sun was joined in the later second century AD by another grandiose temple which is the best preserved of any in the Roman world. It was probably dedicated to Dionysus-Bacchus, and its platform served as a stage for performances of his Mysteries (p. 187). But the crypt, below the flights of stairs leading to this altar platform, foreshadows a Christian church (p. 107), and the colossal fluted pilasters, rising above not one but two tiers of niches in strongly plastic chiaroscuro, echo the painted scenes of theatres in a three-dimensional form which pointed the way to favourite Renaissance designs.54
The splendour of this temple at Heliopolis was equalled or exceeded by the shrine erected by Elagabalus at Rome for his native Sun fetish, whom he raised to supremacy over the other gods (p. 177). This enormous building on the Palatine, now vanished, was renamed after the more traditional Jupiter the Avenger by Elagabalus’ cousin and successor Severus Alexander, whose medallions display its six-column facade surrounded by porticoes and approached by a monumental gateway and flight of steps. Emperors continued to be interested in the planning of towns and colonnaded parks,55 but the age of colossal Roman temples adapting the Greek horizontal-vertical tradition practically came to a close with Aurelian’s restoration of Hadrian’s double shrine of Venus and Rome (p. 166) and with his Temple of the Sun in the Campus Martius, which seems from a drawing by Palladio to have been built in a gigantic rectangular enclosure (approached by two courts) reminiscent of Baalbek.
However, the major architectural effort of the time was lavished on other kinds of building. Conspicuous among these were public Baths. These magnificent structures, of which there were finally eleven at pampered Rome, nine at Constantinople, and further examples in almost all the cities of the empire, displayed much ingenious variety of function, being designed not only for luxurious bathing but for all the activities of an elaborate community centre in which many people of the time spent a substantial part of their day. All the features of the thermal complexes built at Rome by Agrippa, Titus and especially Trajan, with a new elaboration of terraces and ceilings and vaults, were incorporated in the Baths of Caracalla. Begun by Septimius (206), inaugurated by Caracalla, and completed by his successors, this outsize building, or rather group of buildings, has lost its sumptuous decoration; but the ground-plan and part of the massive brick-faced concrete framework are still to be seen. The external elevation must to some extent have lacked unity and logical coherence, though the architect was feeling his way towards a new aesthetic of functionalism based on a three-dimensional play of thrust and counter-thrust. But such ideas were still much more evident in the interior. These halls are so large that man vanishes – for all its human purpose this is the architecture not of humanism but of a new age in which the individual is one of a mass. The main building (750 by 380 feet), flanked by an elaborate enclosure with garden, open-air gymnasium, works of art and every other amenity, could probably accommodate as many as 1,600 bathers at the same time. There was a circular domed hot room, measuring 115 feet across; its ruined apse is still visible. But the central feature of the Baths of Caracalla was a great cross-vaulted hall, measuring 185 by 79 feet and including a swimming pool. The load of the concrete intersecting vaults, with their increased span and assurance, was carried not on a row of columns but on only four enormous piers (in which the classical columns have become non-functional), so that the building is a prototype of medieval cathedrals with their vaulted naves.
Vaults and domes and semi-domes and apses, based on the revolutionary and gradually improved technique of light-weight thrustless concrete, were the peculiar achievement of Roman architecture, and they achieved full expression in the great halls of the Baths.56 Such buildings erected by later third-century emperors, if enough of them had survived, would have illustrated this theme further.57 They would also have demonstrated the increasingly skilful employment of exterior brick facings (without marble or stucco veneers), still to be seen at Philip’s Baths and Theatre at Philippopolis in Trachonitis and in private houses at Ostia.58 A semi-dome in the cold room of the Hunting Baths at Lepcis Magna, of third – or early fourth-century date, shows how this sort of surface enabled mosaics, of which the most substantial examples had hitherto appeared upon floors, to be used also for the decoration of curved upper surfaces, where they were to provide the Byzantine empire with its major religious works of art (pp. 88, 105).59
The Baths which Diocletian and Maximian built on the ruins of a great fire (283) seem to have been nearly twice as large as those of Caracalla. In what remains of the central hall, vaults spring from a horizontal entablature which projects from eight huge granite monoliths.60 Augusta Trevirorum (Trier) was the capital of the westernmost of Diocletian’s co-rulers, Constantius I Chlorus, but it may have been the latter’s son Constantine who completed the Imperial Baths. In a ground plan combining unity with movement, the three arched apses of the hot room created an interior of unusual spatial effects, and at the same time added variety to the plastic form of the exterior which now becomes an organic artistic achievement in its own right. A new feature of recessed window-frames anticipates the forms of medieval gateways; and indeed the whole powerful interpretation of architectural masses exercised its influence on later ecclesiastical design.
The Senate-house (Curia) erected by Diocletian beside the Roman forum adapted many of these ideas to a building which instead of belonging to a large complex of Baths stood by itself. This is a lofty, austere, box-like simplification, a structure reduced to a shell or enclosure of broad planes and lines varied by niches. The large blank façade, crowned by a simple gable, is broken only by the doorway and three large windows near the roof.
The masterpiece of the age was the Basilica Nova nearby. Again free-standing, this building, which is about the size of the Cathedral of Notre Dame at Paris (265 by 195 feet), was mainly constructed by Maxentius but altered by Constantine, who changed the orientation from the long to short sides. Reminiscent of a Sassanian throne-room, the Basilica Nova was based on the bold technical and aesthetic idea of extracting and isolating en bloc the central cross-vaulted hall familiar in Baths, and making this into an independent structure. Until recent experiments such as Diocletian’s Senate-house, free-standing halls, notably market-basilicas – social, judicial and commercial meeting places associated with a forum-had normally been rectangular buildings with colonnaded aisles and flat roofs.61 They had sometimes terminated in apses, and their naves had possessed windowed upper stages extending above the roofs of the adjacent aisles. The vast, vaulted Basilica Nova shares these features; but under the influence of the designs of Baths they are transformed. The 114-foot-high nave, with a daring application of intersecting groin-vaults (which had occasionally appeared at Rome for four centuries past) is illuminated in its upper reaches by a new kind of lighting. This was effected by huge half-circular Romanesque-looking windows, one for each bay, creating a rhythmical relation of window to massive, medieval wall. There were only three bays, separated by huge internal supports which arches across the barrel vaults of the aisles linked to piers projecting from the side-walls. This exercise in the maximum dematerialisation of space can still be imaginatively reconstructed from the three soaring spans of nave and aisles that remain and lead up to the northern apse added by Constantine.
The talent for supremely managed immensity reached its zenith in the imperial palaces which provided the epoch with its principal architectural splendours. Earlier emperors had developed the conception of a palace-city in a park, but their successors may also have been stimulated to their ever more imposing construction by the example of the Parthians and Sassanian Persians (p. 23); who in turn owed the lay-out of their palaces, as well as of circular camp-cities such as Ardashir I’s Firuzabad, to their own Assyrian and Babylonian forerunners. The naved, aisled and vaulted palace halls of the Parthians at Hatra and Asshur ultimately derived their shape from tents that could be closed against the winds. The Versailles of Shapur I (?239–70) was at Bishapur in Fars, a quadrilateral design in the Greek style adorned with carpet-like floor mosaics combining Iranian and western trends.62 But Shapur also built another imposing palace (Taq-e-Kesra) at his capital of Ctesiphon on the Tigris. Its surviving 83-foot-wide elliptical barrel-vault dispenses with supporting arches. Employing brick in Mesopotamia and Persia, and rough-hewn stone and quick-setting gypsum mortar on the plateau, the Sassanians equalled or exceeded contemporary Rome in the structural and artistic boldness of their vaults, cupolas and enormous side-chapels. On the other hand, the limitations of their art and government alike were shown by the monotonous recurrences of bloodthirsty warfare on the stucco and fresco decoration of these vast buildings. More significant is the architectural ornamentation of Ctesiphon, for the over-all simplicity of its design is modified by nonfunctional pattern-making rows of recessed blind arcades. This was one of many elements freely adapted from Greco-Roman lands, and due before long to appear in them again (p. 89).
The first Roman imperial residences of similar type may well be datable to the time of Valerian and Gallienus, though the discovery of their palaces remains the task of excavators of the future. Valerian perhaps began, and Gallienus developed, a camp-headquarters of palatial style at Syrian Antioch, precariously situated at the hub of the eastern defence-system. The equal significance of Mediolanum in the western frontier zone was probably signalised by similar constructions under Gallienus. Mediolanum looked outwards to the dissident, competing empire of Postumus (p. 16), who likewise developed a complex of imperial buildings, subsequently demolished, at his capital of Augusta Trevirorum on the Moselle.
But it was not until Diocletian divided up the empire with three colleagues that palaces were built at these and other centres on a truly massive and extravagant scale. At Antioch, the base for Galerius’ eastern victory and the place of his Triumph, his senior colleague Diocletian designed a new city in something like the circular Persian style (p. 103), though its intersecting streets conformed with Roman military fashion. An insatiable builder, Diocletian endowed this renovated and expanded Antioch with granaries, two temples, several Baths, arms factories and a reconstructed stadium. He also completed and expanded the palace that had been started by Valerian or Gallienus.63 Palmyra, restored from its destruction after Zenobia (p. 20), was another eastern city which received from Diocletian not only extensive military buildings but an imperial palace. This, with a Hall of Audience or throne-room at its central point, stood upon a lofty built-up terrace above symmetrical, camp-like constructions situated on a steeply rising terrain. And yet Diocletian himself lived at neither of those eastern cities, but at Nico-media (Izmit) on which he bestowed new buildings that have not survived but were planned on a scale intended to rival Rome itself.
His co-rulers lived at Mediolanum, Thessalonica and Augusta Trevirorum (p. 98). At Mediolanum, an important cultural and artistic centre, Maximian is likely to have built a splendid palace. At Thessalonica, recent excavations have revealed something of the residence of the Caesar Galerius. This, including a large octagonal hall, lay to the west of a processional street linking the sea with other new buildings. The massive complex included a hippodrome, theatre and colonnades, and the present circular church of St George was almost certainly Galerius’ mausoleum (p. 107). But the best idea of a tetrarch’s court (and the finest collection of Roman buildings north of the Alps) is to be found at Augusta Trevirorum, where Constantius I developed his capital on the site of the residence of Postumus; the city-gate (Porta Nigra) is almost a castle in itself. Constantius’ palace occupied the whole north-eastern part of the city. The so-called ‘Basilica’, a building 280 feet in length and 100 feet in height which originally dates from c. AD 300 and was probably completed by Constantine, has now been recognized as the Hall of Audience or throne-room of the palace, corresponding to Diocletian’s at Palmyra (p. 104). The spacious, timber-roofed hall at Augusta Trevirorum has the aisle-less box-like simplicity of Diocletian’s slightly earlier Senate-house at Rome; the classical orders only survive as niche-frames, on either side of the raised semi-circular apse. This, at the short north end of the hall, is divided from the nave by a chancel arch anticipatory of Christian churches. The thick, concrete walls are lit by two storeys of rounded windows. As in the Roman Basilica Nova, these dramatic internal effects are echoed and equalled by a novel grandeur of external design, in which the outer walls are strengthened and diversified by massive arcade-like projections which rise above both tiers of windows, transforming the surface into an articulated, vertical unity of light and shade.64
Portions of figured frescoes recently discovered in the imperial palace of Augusta Trevirorum show that the heavily ornate ceiling was painted with imitation coffering, of which the eight surviving panels represent Cupids, and women handling jewels. These fragments serve as a reminder that the well-known catacomb pictures of this and earlier periods were accompanied by a long and diverse series of pagan counterparts, usually more technically skilful than the Christian paintings but not often so emotionally convincing (p. 214).65
Another outstanding art which reached its decorative culmination during the third and fourth centuries AD was that of the paviment-mosaic, which was still more frequent than mosaics on vaults and walls (p. 102).66 In general, ‘carpet’ designs extending all over the floor increasingly superseded the rug, mat or panel conception. Nowhere are these mosaics more spectacular than in the large palace discovered not long ago at Piazza Armerina near Henna in Sicily. Excavation has disclosed 42 polychrome pavements comprising 30 million pieces of mosaic spread over 3,500 square yards. Although most of the designs deal monotonously with the royal and imperial sports of hunting and the massacres of animals which accompanied them,67 the decorative possibilities of this medium are explored through contrasts between lively, precise, naturalistic, narrative details and a rival tendency towards schematic distortion of natural shapes.
Oblivious of nature in the spirit of Hadrian’s villa at Tibur (Tivoli) and late Roman houses at Ostia,68 the conglomeration of Piazza Armerina reveals an inorganic, twisting, triple-lobed design full of surprises and restless convolutions, worked out with a ‘persistent deviousness, eternal changing of direction, and hiding of the goal’. The mosaic portrait of the lord of the palace, in his purple-ornamented tunic and long grey trousers, has a good deal in common with coins and statues of Diocletian and Maximian and their colleagues, and when these two Augusti both abdicated in 305 this may have been one of the mansions to which Maximian reluctantly, and as it turned out by no means finally, agreed to retire – though his main abode was in Lucania.69
Whether or not that was the purpose of Piazza Armerina, Maximian’s senior colleague Diocletian abdicated once and for all, and went to live at Salonae (Split) in Dalmatia; and his residence there has survived on a far more impressive scale than any other. This was the project, supported by the appalling taxation of the time, upon which Diocletian spent the years of his retirement, outdoing the numerous palaces of his predecessors and younger colleagues and Persian rivals. This blend of civil and military architecture, much more compact than Piazza Armerina, amalgamated the public rooms of a palace, the residential quarters of a great Dalmatian villa or a commander-in-chief’s house,70 and an inward-looking impregnable fortress, guarded by a wall that was studded by square and polygonal towers.71 Central to this ruthlessly axial plan is a main avenue which leads through the palace city up to the focal Hall of Audience. Beyond a colonnaded courtyard (atrium), the main surviving feature of this throne-room is its three-bayed columnar façade, crowned by a gabled Pediment of Glorification. Over the middle columns curves an arch, beneath which, as if framed by the vault of heaven, Diocletian made his appearances and received homage like a divine effigy.72 Behind the courtyard was a domed circular vestibule with four small apses, and behind that again the shrine-like Hall of Audience itself, where the retired, revered emperor sat, jewelled and haloed, beneath a columned canopy.
On either side of the courtyard approaching these buildings stand arcades of which the arches are not surmounted by horizontals but spring straight from the Corinthian columns in an energetic, un-classical fashion, which had occasionally been seen since Augustan times73 but was now fully exploited in the form which was to lead to the main architectural styles of later Europe. Another forward-looking type of colonnade appears on Salonae’s richly decorated Golden Gate, which has a row of seven dummy arches like those at Shapur’s Ctesiphon (p. 103). This gate, once flanked by towers, stands at the far north end of the processional avenue which leads through the town to the Hall of Audience at its opposite extremity.74 The south face of the Hall looked directly upon the sea, and here, between two square towers, the wall is broken by a gallery with a loggia at each end and in the centre. The gallery has forty-two arched windows; between them are engaged columns which rest upon blocks (corbels) projecting from the wall for the first time in the known history of architecture.75
In the middle of the whole rectangular complex, the courtyard leading up to the Hall of Audience was flanked on one side by almost the last recognizable Roman temple76 – and on the other by the building which was to contain Diocletian’s tomb.
This mausoleum illustrates a fertile contemporary trend towards domed constructions. There were many Greco-Italian precedents for such buildings, including Etruscan funeral monuments, round temples76 and large thermal halls, such as the circular hot room of Caracalla’s Baths (p. 101). Recent examples had shown growing expertise in dealing with a problem beyond the range of earlier Greek architects. That consisted in placing a dome over a building which was square or polygonal. During the second century AD there were attempts to unite these two shapes by means of triangular concave sections (pendentives) joining the curved base of the dome to the angles of the walls.77 The problem approached its final solution in a marble pendentive from Septimius’ four-way arch at Lepcis Magna, and in two small domed octagonal halls (externally square) on the periphery of the Roman Baths of Caracaila.
A highly sophisticated specimen of these centralised buildings, straining the classical Orders as far as they would go, is the small so-called ‘Temple of Venus’ at Heliopolis (Baalbek), perhaps built in the second and rebuilt in the third century AD. This elegant baroque shrine, aptly imitated by Borromini,78 is round, but the circle is broken by five concave niched recessions between columns. Although most third-century Roman buildings have vanished, coins and medallions show a number of unknown centralised temples,79 and a diversity of ribbed or plain vaults and curves is detectable from the scanty remains of various edifices in Rome and its suburbs. At Salonae, the vestibule of Diocletian’s palace is domed and circular, but the dome of his mausoleum nearby is internally circular while presenting a façade and external colonnade which are both octagonal. Inside, there are eight deep wall-niches alternatively rectangular and curved.
The Middle Ages are announced by the crypts which now appear not only in an occasional temple of longitudinal shape (p. 100) but also in these centralised buildings, notably the circular Diocletianic ‘Tomb of the Gordiani’ at Rome.80 Its walls are pierced with rounded openings for the admission of light. A small ten-sided Roman structure of the same epoch, with another fictitious name (‘Temple of Minerva Medica’), again possesses large rounded windows in each of its sides. This building has not only four closed apses, which are a familiar feature of the period, but also five recesses which open up the interior through curving columnar arcades that perforate and dematerialise the outer walls in a fashion not apparently seen again until the mid-fifth century.
When these circular or centrally planned edifices were mausoleums, they were the immediate ancestors of Christian buildings commemorating martyrs and serving as burial-places and baptisteries and churches.81 Owing to the increased connection of religious services with martyrs and holy sites, Constantine joined this type of building onto rectangular churches or basilicas (p. 110): when, later, the two formulas were completely integrated, the result was Justinian’s Santa Sophia. At Constantine’s Grotto of the Nativity at Bethlehem, excavations have shown that an octagon was attached to the east end of a rectangular church hall, and the original Church of the Holy Sepulchre at Jerusalem (Golgotha) (328–36) had a circular martyr’s shrine (upon the site of a Jewish tomb chamber) in the middle of an apsed basilica. His new capital of Constantinople (p. 99) did not at once become a major architectural centre, but Constantine built its first church of the Holy Apostles to combine in novel fashion the functions of his own mausoleum and a Martyrium of the Apostles.82 This was a cross-shaped structure, and under the central drum, surmounted by a conical roof, were placed for a time the remains of the emperor, who was venerated as the thirteenth of the Disciples.
These churches have now vanished, and so has another important centralised building which Constantine constructed at Antioch. Here, next to the imperial palace on the Orontes island in the centre of the city, he began and nearly completed the magnificent Golden Octagon, dedicated to Harmony, the divine power that unites Universe, Church and Empire (327–41). Descriptions and a sketch on a floor mosaic suggest that the gilded wooden roof was either pyramidal or, perhaps from the outset, a dome,83 and that this central area was surrounded by a colonnaded aisle in two storeys. The Golden Octagon was not a cathedral or a martyr’s shrine but a palace church, and the ancestor of similar octagonal, galleried palace chapels built by Justinian at Constantinople and by Charlemagne at Aachen.84
These and many other buildings of Constantine were the products of an architectural revolution (c. AD 315), proceeding from the religious revolution which had made Christianity supreme (p. 237) and accompanied by official encouragement to engineers and architects.85 The round or polygonal churches provided one result of these new developments, but their principal manifestation was the new Christian basilica. These successors of humble house-churches86 were oblong longitudinal buildings – often entered from a large external courtyard – containing side-aisles separated from the nave by arched colonnades. Above these colonnades, since the nave was higher than the aisles, came brick walls standing directly on the arches, and usually pierced by windows. Beyond the chancel arch was an apse, rising behind the canopied altar and containing the bishop’s throne (cathedra). The main part of these basilicas, however, was not vaulted; they had wooden roofs, open or concealed by a flat ceiling. The great Roman cross-vaults seemed too earthly and reminiscent of pagan buildings, and they would have slowed down the single irresistible tide of nave and aisles which drew the eye towards the altar and the apse.
These resplendent buildings, which set so historic a pattern for the future, owed their structure and window arrangement to the colonnaded pagan basilica which had served as market, court and meeting place – with a tribunal where the bishop’s seat was now. And yet the strong axial direction of the churches towards their altar was quite different from the passive orientation of the pagan building. The Christian basilica, with its internal colonnades, has been described as a Greek temple turned inside out.87 But one of its immediate models was provided by the Halls of Audience in recently constructed palace-cities such as Augusta Trevirorum and Salonae. Just as the elaborate palace ceremonial was incorporated into Christian liturgy (p. 237), so too the Christian altar beneath its canopy was like an emperor’s throne, and the triumphal chancel-arch echoed the gable of imperial glorification upon the Hall of Audience. The courtyard of the Christian churches, too, once had its forerunner and counterpart outside the Basilica Nova of Maxentius (p. 102). And from there the imposing doors of the Christian basilica disclosed a dignified, visionary, spiritualised interior which interpreted the mysteries of heaven while remaining mindful of the disciplined Roman past. Many of Constantine’s basilicas were entered from the west, so that the rising sun fell on a celebrant as he stood before the altar facing his congregation. For the space-creating essence of the revelation is incorporeal and insubstantial Light: there is holy penumbra below, but radiant luminosity bathes the building and its worshippers from above (p.181).
Constantine’s dramatic basilicas, erected in many parts of the empire, abounded in this light and colour, enhanced by gilding and other precious decoration. Yet there is nothing to be seen of his major monuments today. Some have disappeared, but most became so famous that new churches were subsequently erected on the same sites. This, for example, was the fate of his wide, double-aisled church of Holy Wisdom (Santa Sophia) at the new capital of Constantinople; it was replaced by Justinian’s building. Constantine’s Lateran Church, the cathedral of Rome, has likewise been supplanted by a series of successors. This Basilica Constantiniana, dedicated at first to our Saviour,88 was laid out shortly after the donation of the neighbouring palace to the recently recognized pope and bishop (c. AD 313). The church had a nave flanked not by a single side-aisle on either side but by a pair. These, adjoined at the east end by small wings or sacristies like miniature transepts, were supported by rows of huge columns of yellow and red marble, and speckled green on the outside rows. The building terminated in a lofty projecting apse, with a huge screen of silver (adorned by solid silver statues) extending across its entrance. ‘The congregation saw Christ the Teacher seated and flanked by his apostles, while the clergy were faced by a Christ Resurrected, enthroned between four angels. Like the emperor, then, Christ revealed himself under the upswept lintel in different but complementary aspects to the people and high officials of his court.’89
Then, near Nero’s Vatican Circus, Constantine built the Basilica of St Peter (c. 333?-37). This church, before its replacement in the sixteenth century, resembled the Lateran in possessing resplendent, colourful decorations and two aisles on each flank of its long, tall nave. But between these and the apse to which they led there was a massive transept extending on either side, filled with the light from sixteen great windows in contrast with the darkness of the aisles. This is a novel response to the cult of martyrs which led Constantine, elsewhere, to blend longitudinal basilicas with centralised shrines (p. 108). For the church stood on the site which had long been believed to be the burial place of St Peter (p. 231). Since the crowds who came to venerate the martyr were too great to be accommodated in any less spectacular way, Constantine erected this spacious transverse annex – a covered cemetery or catacomb moved above ground, and merged with the largest building and holiest sanctuary in the western church. Because of this exceptional purpose, the architectural feature of a continuous transept was at first rarely copied elsewhere,90 until the architects of Charlemagne brought it into more extensive use.
29 A red porphyry bust of Maximinus II or Licinius, from Athribis in the Nile delta. Such is the strange, formidable spirit of Diocletian’s Tetrarchy
30 Constantine the Great. These colossal heads, with their immobile inhuman gaze, are cult objects, mirroring the eternal order
Coins and medallions
31 Pertinax (193), who failed to replace the excesses of Commodus by a regime of austerity. Providence is seen raising her hands in worship of a star
32 Septimius’ son Geta, wearing the crown of the Sun-god, lifts his hands in the gesture of benediction inherited by Christian bishops. C. 200
33 Nicopolis ad Istrum (now in Bulgaria), dangerously near the Danube border, shows, under Septimius, its massive city-gate, in this new era of fortified towns
34 Caracalla (211–17), whose exceptionally fine baroque portrait-busts are emulated on his coins. He calls himself ‘Antoninus Pius’, but, unlike his forerunner, was nervous, disagreeable and brutal
35 The Syrian Julia Maesa, who raised her perverted grandson Elagabalus to the throne and then allowed or encouraged his murder. Reverse: Piety
36 Severus Alexander’s elaborate precinct of Jupiter the Avenger (previously Elagabalus’ Temple of his Sun-god) has now completely vanished
37 The Greek university town of Tarsus (S. Turkey) portrays Gordian III (238–44) in a wiry, linear style which reached the official coinage half a century later
38 Phrygian Apamea (Dinar in Turkey), under Philip, shows Noah’s Ark. The local Jewish community, important enough to influence the coinage, believed the Ark had landed nearby
39 On this golden medallion, a prize at Macedonian games (AD 242–3), the eyes of the legendary Alexander the Great roll upwards to heaven and the sun
40 Decius’ depiction of the two Pannonias, his own Danubian homeland, illustrates the new supremacy of this reservoir of soldiers and emperors
41 Wishful thinking, or pious hoping: Peace Everywhere (VBIQVE PAX) when the empire was rent in fragments under Gallienus (253–68)
42 Coin-portraiture can still be individual under Aurelian. Close-cropped and with unshaven military jowl, he celebrates the recovered unity of the empire by a figure of Concordia
43 Diocletian, at his capital Nicomedia (Izmit), introduces a brutally forceful cubic portraiture. Jupiter stands for an anti-Christian return to the old gods
44 Probus (276–82), with Aurelian the main author of Rome’s military recovery, is represented on coins and medallions in many splendid outfits
45 Probus with the Sun-god his Companion (COMIS): now the most revered deity in the pagan pantheon
46 The usurper Carausius, in Britain, is no nationalist, for he displays the Wolf and Twins, inscribed Revival of the Romans (RENOVAT. ROMANO.)
47 Constantius I Caesar has suppressed the dissident British state, and is seen entering London as Restorer of the Eternal Light (296)
48 Another rebel ‘emperor’, Domitius Domitianus in Alexandria, imitates Diocletian’s ‘Genius of the Roman People’, one of the last great pagan rallying cries
49 Maxentius’ son Romulus died in boyhood, and according to an ancient pagan tradition, now about to end, was made DIVVS, a god of the Roman state. C.310
50 Constantine’s fellow-emperor and enemy Licinius (312–24) and his son are shown haloed, in frontal poses which herald the Byzantine icon
51 Constantine, at his new capital Constantinopolis (CONS.). The standard, bearing the letters XP (Christos) and inscribed ‘The National Hope’ (SPES PVBLIGA), crushes the serpent of evil
52 Coining at Thessalonica (Salonica) in honour of his subservient senate (SENATVS), Constantine wears an embroidered gala costume equal to any Persian monarch’s
The Persian kings
53 Ardashir (Artaxerxes I: c. 223–39), founder of the Sassanian empire which was a far more formidable enemy to Rome than its Parthian predecessor
54 Shapur I (c. 239–70), the scourge of Rome and captor of its emperor Valerian. On the reverse is the Fire-Altar of the Zoroastrian state religion
55 Bahram I (c. 273–7), who arrested the greatest preacher of the, age, Mani, as an opponent of the royal headship of the church. Mani died in chains
Silver and gems
56 A silver image of Zeus, now the object of almost monotheistic cult, from Asia Minor, AD 180: foreshadowing the Christ and saints of Byzantium
57 This Sassanian silver-gilt vase still shows strong Greek influences, but Persian art gradually became more national and Iranian
58 Sard (deep red semi-precious-stone) with intaglio portrait of a young man of the early third century AD
59 Pendant cameo with the heads of Diocletian and Maximian or their Caesars. C. AD300
60 The Arch of Marcus Aurelius, completed after his death, shows a new feeling for the horrors of war and the sufferings of German prisoners