Constantine the Great Rules
Emperor Constantine I is often credited with converting the Roman Empire to Christianity. In fact, though he ended the persecution of Christians and eventually converted, some historians debate the true nature of his faith.
His association with Christianity began with a fateful battle for control of the Western Roman Empire. Constantine faced Western Roman Emperor Maxentius at the Tiber River's Mulvian Bridge in A.D. 312. Fourth-century historian and bishop Eusebius of Caesarea reported that before the great battle Constantine saw a flaming cross in the sky bearing the words "in this sign thou shalt conquer." Constantine did indeed conquer, routing and killing his enemy on a day that loomed large not only for the emperor but for the Christian faith.
The next year Constantine, now the Western Roman Emperor, and Eastern Roman Emperor Licinius signed the Edict of Milan, which finally ensured religious tolerance for Christians. The agreement granted freedom of worship to all, regardless of deity, and brought an end to the Age of Martyrs, which had begun after Jesus' death. Christians were also given specific legal rights such as the return of confiscated property and the right to organize dedicated churches.
After unifying the Roman Empire under his rule in A.D. 324, Constantine rebuilt his seat of his power in largely Christian Byzantium, which was renamed Constantinople and today is Istanbul. The growth of a Christian ruling class under Constantine ensured the faith's increasing and enduring prominence through the Roman, and later Byzantine, Empire.
Constantine convened and took part in the first meeting of Christian churches, the Council of Nicea, held in 325 in what is today Iznik, Turkey. He hoped to help church leaders find common ground on some contentious aspects of Christian doctrine. Chief among these issues was the relationship and relative divinity of God the Son (Jesus) and God the Father. Arianism was popular during this period. This Christian belief championed by Arius, a priest of Alexandria, Egypt, held that Jesus, though the Son of God, was inferior to God the Father.
The Council of Nicea established the equality of Father and Son and documented this in a creed, or universal statement of faith, to which all but two attending bishops agreed. The dissenting bishops were exiled, as was Arius himself. After this council, orthodox Christians agreed on the critical point that Jesus and God were equally divine and created of the same substance. The council also condemned the practice of money lending by clerics and attempted, unsuccessfully, to standardize the date of Easter.
Ancient Christian historians enthusiastically portrayed Constantine as a pious Christian convert. In later years some scholars suggested that the emperor simply used the faith to his political advantage. The truth may lie somewhere in between, but Constantine's importance to his adopted religion is beyond doubt.