1. The Architecture of Christian Rome

2. In July 285, the Emperor Diocletian declared Maximal, a colleague from Illyricum (Serbia), his co-emperor. Each emperor would have his own court, his own military and administrative faculties, and each would rule with a separate praetorian prefect as chief lieutenant. Maximian ruled in the West, from his capitals at Mediolanum (Milan in Italy) or Augusta Treverorum (Trier in Germany), while Diocletian ruled in the East, from Nicomedia (Izmit in Turkey). The division was a pragmatic response to continual frontier wars: the Empire was called "indivisible" in official proclamations and both emperors could move freely throughout the Empire. Diocletian divided the Empire again in 293, appointing two Caesars (junior emperors) to rule over further subdivisions of East and West. Each would be subordinate to their respective Augustus (senior emperor) but would act with supreme authority in his assigned lands. This system would later be called the Tetrachy. Splitting the Roman Empire

4. Sculpture of the Four Tetrachs c.300 ad. Now at S. Marco, Venice. Looted from Constantinople in 1204

5. Constantine ‘the Great’ Constantine was declared ‘Augustus’ of the West in Eboracum (York ) in 306 ad. Although accepted by Galerius (Augustus of the Eastern Empire), his position was opposed by Roman nobles and he spent the next 19 years in civil wars with the other Tetrachs. He finally defeated the last ‘Eastern’ Caesar at the Battle of the Milvian Bridge in 325, becoming sole head of the whole Roman Empire. He attributed his successes to the power of the Christian God, under whose Chi-Rho banner he had defeated his chief rival Maxentius in 312. So began the ‘Christianisation’ of Europe. In order to reintegrate the pagan, Greek- speaking Eastern Empire with the Latin- speaking, Christian West, Constantine made the Greek city of Byzantium into a new imperial capital – Constantinople – in 330 ad.

11. Cubiculum of Leonis, Catacomb of Commodilla, Rome, late 4th c

13. Basilica of Maxentius and Constantine, Rome 308-12 ad

16. Basilica of Maxentius Reconstuction

18. Old St Peter’s, Rome 326 – 360 ad

19. Cubiculum of Leonis, Catacomb of Commodilla, Rome, late 4th c

25. Old St. Peter's, Cross section drawing looking east by G. Grimaldi, 1619

26. The Basilica of Saint Sabina at the Aventine 422 ad

28. ‘ Basilica of Constantine’ (actually the throne room of the Imperial Palace), Trier, 310 ad

31. Santa Costanze, Rome (orig. mausoleum of Constantia and Helena), 350a d