History of the East–West Schism
Disunion in the Roman Empire further contributed to disunion in the Church. The Emperor Diocletian famously divided the administration of the eastern and western portions of the Empire in the early 4th century, though subsequent leaders (including Constantine) aspired to and sometimes gained control of both regions. Theodosius the Great, who established Nicene Christianity as the official religion of the Roman Empire (see Edict of Thessalonica), was the last Emperor to rule over a united Roman Empire. Following his death in 395, the division into western and eastern halves, each for a few decades still under its own Emperor, was never reunited.
Imperial cult of ancient Rome
Constantine's nephew Julian, Rome's last non-Christian emperor, rejected the "Galilean madness" of his upbringing for a synthesis of neo-Platonism, Stoic asceticism and universal solar cult and actively fostered religious and cultural pluralism. His restored Augustan form of principate, with himself as "primus inter pares", ended with his death in 363, after which his reforms were reversed or abandoned. The Western emperor Gratian refused the office of "pontifex maximus" and, against the protests of the Senate, removed the altar of "Victoria" (Victory) from the Senate House and began the disestablishment of the Vestals. Theodosius I briefly re-united the Western and Eastern halves of the Empire, officially adopted Nicene Christianity as the Imperial religion and ended official support for all other creeds and cults. He refused to restore "Victoria" to the Senate House, extinguished Vesta's sacred fire and vacated her temple. Even so, he accepted address as a living divinity, comparable to Hercules and Jupiter, by his overwhelmingly pagan Senate. After his death the sundered Eastern and Western halves of Empire followed increasingly divergent paths: nevertheless both were Roman and both had emperors. Imperial ceremonial – notably the Imperial "adventus" or ceremony of arrival, which derived in greater part from the Triumph – was embedded within Roman culture, Church ceremony and the Gospels themselves.