Constantine converts to Christianity in 312

Another important event in Ancient Rome is that Constantine converts to Christianity in 312. In 306, Constantine became the tetrarch of the Roman Empire. He waged numerous wars against the other tetrarchs. He first defeated Maxentius in 312. In 313, he issued the Edict of Milan, which granted Christians the freedom to practice their faith. Constantine became a Christian, thereby enforcing the Christian faith. He began the process of Christianizing the Empire and Europe, which was completed by the Catholic Church in the Middle Ages. He was beaten 306-308 by the Franks and the Alamanni. In 324, he conquered another tetrarch, Licinius, and regained control of all empires as they had been before Diocletian. To commemorate his conquests and the importance of Christianity, he rebuilt Byzantium and called it Nova Roma ("New Rome"); however, the city quickly became known as Constantinople ("City of Constantine").

Julian's reign, which strove to reestablish Classical Roman and Hellenistic religion under the influence of his adviser Mardonius, only briefly interrupted the series of Christian emperors. Constantinople served as the Empire's new capital. In truth, Rome had lost its major position since the Third Century Crisis (Mediolanum was the western city from 286 to 330, until the reign of Honorius in the 5th century, when Ravenna was named the capital). Constantine's administrative and monetary reforms, which reunited the Empire under one ruler and rebuilt Byzantium, altered the ancient world's high period.