Constantine the Great (CE 272-337)’s main claims to fame for the modern reader are: he was the first Roman emperor to convert to Christianity and he issued the Edict of Milan (313) that granted religious freedom to all religions in the Empire, including Christianity.
Diocletian (244-311) complicated the succession to the imperial crown by creating posts for two senior emperors and two junior emperors. Each senior emperor was called “Augustus.” One ruled the eastern empire and one the western. Each “Augustus” had a “Caesar.” It wasn’t long until all four jobs spawned swarms of hopeful successors.
Constantine entered the imperial pecking order in 293 when his father Constantius became one of the Caesars.
Although the dates for his reign are given as 306-337, Constantine did not become the sole emperor of Rome until 325 when he executed the last two contenders from the multiple-emperor pool, one of whom was his sister’s son.
The story of Constantine’s conversion to Christianity is usually related in connection with his battle against Maxentius at the Milvian Bridge near Rome in 312.
One version of the story states that the night before the battle Constantine had a dream in which a messenger told him “to mark the heavenly sign of God on the shields of his soldiers…by means of a slanted letter X with the top of its head bent round…”
This was the Chi Rho symbol representing the first two letters of the word Christ.
According to another version, Constantine had a vision “while marching at midday”:
he saw with his own eyes in the heavens a trophy of the cross arising from the light of the sun, carrying the message, In Hoc Signo Vinces or “In this sign, you will conquer.”
In this version of the story, the dream comes the night after the vision. In the dream Christ shows Constantine the labarum, the Chi Rho symbol in the form of a Roman standard.
Constantine’s mother Helena was a Christian, but he was a practicing pagan for most of his life, even after the Chi Rho vision.
Like all emperors before him, Constantine held the office of pontifex maximus, chief priest of the Roman religion. The triumphal arch he built to celebrate the victory at the Milivian Bridge was sculpted with pagan imagery, but no Christian symbols. In 321 he decreed that everyone, including Christians, must observe the “venerable day of the sun” and pay cult to Sol Invictus.
Constantine interested himself in church politics and took sides in matters of heresy. He was a man who liked order and discipline. He took it upon himself to convoke the Council of Nicea in which he called together all important Christian leaders and told them to agree on doctrine. The Council condemned the form of Christianity known as Arianism. Later on, Constantine led an army of “orthodox” Christians on a crusade against Donatist Christians in Africa.
Constantine showed a lot of favor to Christianity, subsidizing many churches and supporting the Church financially and legally, but he did not make Christianity the sole religion of the Empire. That would wait until the emperor Theodosius I abolished the Edict of Milan and criminalized not only pagan practice, but religious debate of any kind.
As for becoming a Christian, Constantine postponed baptism until he knew that he was dying; he chose his cousin Eusebius of Nicodemia–an Arian Christian–to baptize him.
As my dear Dr. Johnson says,
Inconsistencies cannot both be right; but, imputed to man, they may both be true.