In 303, the Emperor Diocletian ordered the churches pulled down and the scriptures burned — the fiercest persecution Christianity had ever faced. Ten years later, the empire legalized it. Within a single lifetime, the persecuted sect became the state religion. No reversal in history was faster — or more complete.
The story in images
The discovery
In 313 AD, the Edict of Milan — issued by the emperors Constantine and Licinius — granted religious toleration across the Roman Empire and ordered the restitution of confiscated Christian property. Christianity, illegal and intermittently hunted for nearly three centuries, was legal overnight. Within two generations it would be mandatory.
By whom
By Constantine I, who won the Western Empire at the Milvian Bridge outside Rome in 312 — fighting, he later said, under a vision of the cross with the words in hoc signo vinces, ‘in this sign, conquer.’ By Licinius, his co-emperor in the East, co-signer of the edict. By the bishops — suddenly courtiers instead of fugitives — and finally by Theodosius I, who finished the job: in 380, the Edict of Thessalonica made Nicene Christianity the official religion of the Roman Empire.
How it happened
Victory first, theology second. Constantine marked his soldiers’ shields with the Chi-Rho — the first two letters of ‘Christ’ in Greek — and marched on Rome. The Edict of Milan followed: toleration for all religions, Christianity named first among them. Constantine then summoned the Council of Nicaea in 325 to settle the faith’s internal quarrels — the Nicene Creed, still recited today, was its product — and poured imperial money into basilicas while the bishops poured converts in. The machinery of state followed the money: clergy exempted from taxes, bishops given courts, pagan sacrifices first discouraged, then — under Theodosius in 391–392 — banned. Temples closed; the Olympic Games, a pagan festival, were suppressed.
The shockwave: how it changed the world
Christianity reshaped the furniture of time itself: the seven-day week with its Sunday rest, the dating of Christmas and Easter, the saints’ days that became Europe’s holidays — the calendar on every wall is, in part, the Church’s calendar. Canon law shaped Western ideas of marriage, contract, and justice; monasteries preserved the classical texts through centuries when no one else could read them; bishops became the administrators of the post-Roman West.
The faith split the old empire in two — Latin Catholic West, Greek Orthodox East — and the schism of 1054 still draws a civilizational line across Europe. Missionaries carried the cross to Ireland, to Germany, to the Slavs, and eventually — on the hulls of European ships — to the Americas, Africa, and Asia: the most successful expansion of any idea in history.
Church and state — united, then warring, then separated — became Europe’s defining tension, producing everything from the Crusades to the secular republic. And seventeen centuries after Nicaea, the Creed is still recited every Sunday by hundreds of millions, the holidays still order the world’s year, and 2.4 billion people still call themselves Christian. Rome knelt once. It never stood back up.