The Edict of Milan (313)
In brief
In 313 the emperors Constantine and Licinius agreed at Milan to grant Christians — and everyone else — the freedom to practice their religion openly, and ordered confiscated church property restored. It is often called the moment Christianity was "legalized," and after nearly three centuries of persecution that is roughly true. But it is important to be precise: the Edict of Milan granted toleration to all religions. It did not make Christianity the religion of the empire; that came seventy years later.
What changed in 313
The great persecution launched by Diocletian in 303 had been the fiercest the Church ever faced from Rome — churches razed, Scriptures burned, clergy imprisoned, believers killed across the empire. It was still fresh when, in 313, the two ruling emperors met at Milan and reached an agreement about religion. Its terms, preserved in the historian Lactantius, ordered "that the Christians and all others should have liberty to follow that mode of religion which to each of them appeared best," and further commanded that property seized from the Christians during the persecution be given back.
For the Church the practical effect was immense and immediate. Bishops could meet openly, buildings could be built, and the faithful could come up out of the catacombs into the light. The age of the Roman persecutions was, with one brief exception, over. Within a dozen years the emperor would summon the bishops of the world to the first ecumenical council at Nicaea — something unthinkable a generation earlier.
Toleration, not establishment
It is easy, and wrong, to compress the fourth century and say that in 313 "Constantine made Christianity the state religion." The Edict of Milan did nothing of the kind. Its logic was toleration: it freed Christians and the adherents of every other cult to worship as they chose, so that (in the document's own reasoning) whatever divinity there was in heaven might be favorable to the state. Paganism remained legal and public; Constantine himself was baptized only near the end of his life.
Christianity became the official religion of the Roman Empire only in 380, under the emperor Theodosius, whose Edict of Thessalonica declared Nicene Christianity the faith of the empire. The two dates should be kept firmly apart. Milan (313) opened the door to freedom; Thessalonica (380) is where the empire crossed the threshold and became officially Christian. Conflating them credits — or blames — Constantine for a settlement that was still two generations away.
What it meant for the Church
The change of fortunes was a mercy, and the Church received it as one; the blood of the martyrs had, as Tertullian foresaw, borne fruit. Yet Orthodox memory of Constantine is measured rather than triumphant. The tradition honors him — with his mother, St. Helen — as "Equal-to-the-Apostles" for ending the persecutions and convening Nicaea, while remaining clear-eyed that imperial favor brought its own temptations, and that the close partnership of Church and emperor later called symphonia would prove a mixed inheritance.
What is beyond dispute is the hinge that 313 turned. A persecuted minority worshiping over graves became, within a century, the public faith of the Mediterranean world, free to build, to teach, and to gather her bishops in council. The theological clarifications of the seven councils and the flowering of Christian worship all presuppose the freedom that the Edict of Milan first secured.