During the 4th century Rome broke into two and started to get disintegrated. The state adopted Christianity and Constantine was the first Christian emperor. He carried the political center from Rome to Constantinople. Before this division of the Roman Empire, Christianity was an underground religion, banned and practiced in places like catacombs and caves with artistic designs only on the inside. Starting with 4th century…, the migrations of the Germanic tribes and their arrival in Europe caused great troubles to the Roman Empire, eventually ending it. The eastern part of the empire survived as Byzantine Empire while the arriving tribes in the west were starting to develop their Christian kingdoms.
Before the start of a kingdom in the east, two sons of tetrarches (4 rulers, 2 in the east, other 2 in the west) Constantine and his rival Maxentius were in Rome, in competition, building basilicas. Constantine’s basilica in Trier is closer to the traditional way (and we can observe the resemblance with later structures like St. Sophia’s Church shown above) but Maxentius’ basilica was quite different, resembling an aqueduct.

And then we are introduced to the spolia tradition which is when some specific stones and reliefs on one structure is dated very older than the rest because it’s been taken out from another structure, a sort of recycling. The arch of Constantine was decorated also in this matter. It was made for Constantine to show gratitude for almost because he supports Christians.
In return, Constantine built a cathedral in Rome. It was built very carefully not to resemble pagan temples and followed the route of Constantine’s work in Trier.
After Constantine left Rome, somehow the church continued to gain importance. More so, after the Visigoths entered Italy and started plundering as Alaric, the leader of Visigoths ordered the churches to be left unharmed. Rome held on after that, building probably the last classical churches before the successive invasions of Ostrogoths and Vandals expired the west of the Roman Empire. Old temples like Partheon which used to be dedicated to all gods, went under elegant transitions into Christian shrines. When Rome was having a hard time, Milan became the new center for Christian churches for a brief time.
Constantine, in the east produced the first Roman city plan to include churches as a primary urban component. In Constantinople, three major church types were established: the aisled basilica, the central-plan memorial church and the pavilion-like baptistry. Constantine’s city succeeded beyond all expectations as the new Rome.
Hagia Sophia, the grand structure of Constantinople, went under a lot of reconstruction due to riots, structural concerns and personal ambitions. Like most early churches Hagia Sophia did not have a real façade. It seemed like a great bulging mass. Unlike the Ziggurats or Greek temples, its figure cannot be reduced into a simple figure with proportinal elements. Although the reconstructions after earthquakes and collapses, and even after its transformation into a mosque, Hagia Sophia preserved new Rome’s genius loci, the spirit of the place.