Constantine's Conversion and the Edict of Milan

The event

After Diocletian's retirement, the elaborate power-sharing system he had set up to govern the empire collapsed into a fresh round of civil wars among rival claimants to the throne. One of these claimants, Constantine, marched on Rome in AD 312 to face his rival Maxentius at the Milvian Bridge just outside the city. According to the church historian Eusebius (who claimed to have heard the story from Constantine himself years later) and the writer Lactantius, Constantine experienced a vision before the battle — a cross of light in the sky, or a sign shown to him in a dream — accompanied by words to the effect of 'in this sign, conquer.' Constantine had his soldiers mark their shields with a Christian symbol and won a decisive victory, becoming master of the western empire.

The following year, AD 313, Constantine met his eastern co-emperor Licinius in Milan, and together they issued what history remembers as the Edict of Milan, formally granting freedom of worship to Christians and all other religions across the empire, and ordering the restoration of confiscated church property. Almost overnight, a faith that had been legally vulnerable — and, within living memory, violently persecuted under Diocletian — became not just tolerated but increasingly favored, as Constantine went on to fund church building, exempt clergy from certain civic burdens, and involve himself personally in the church's affairs.

Honest history requires a note of caution here: scholars have long debated exactly how sincere and how theologically developed Constantine's own personal faith was — he was, notably, only baptized on his deathbed in 337, a practice not unusual for the era but one that leaves his inner convictions genuinely uncertain to historians. What is not in serious doubt, however, is the historical reality of the vision account, the battle, and above all the immense, providential turn the Edict of Milan represented: an empire that had fed Christians to lions a decade earlier now stood ready to become, within a generation, an officially Christian empire.

Dating

The vision account comes from Eusebius (Life of Constantine) and Lactantius (On the Deaths of the Persecutors), written within Constantine's lifetime or shortly after, though the two accounts differ somewhat in detail (a daytime sky-vision versus a night dream). Historians continue to debate the depth and timing of Constantine's personal conversion — he was baptized only on his deathbed in 337 — but the battle itself and the legal effect of the Edict of Milan are well established.

Other witnesses

• Eusebius, Life of Constantine 1.28
• Lactantius, On the Deaths of the Persecutors 44

Further reading

• Catholic Encyclopedia (1913): Constantine the Great
• Christian History Magazine 57: Converting the Empire — free full issue