In AD 313, Constantine the Great issued a decree that would reshape the moral landscape of Europe. The Edict of Milan, agreed with his co-emperor Licinius, ended centuries of persecution and allowed Christians to worship freely. Just sixty-seven years later, Emperor Theodosius went further with the Edict of Thessalonica in AD 380, making Christianity the official faith of the Roman Empire.

Between these two edicts, Rome transformed itself from persecutor to protector, and finally to promoter of the Christian church. The consequences would ripple through Western civilisation for centuries.

Christianity began as a small and often suspect sect within the Roman world. Followers of Jesus of Nazareth proclaimed loyalty to one God above all others, a claim that seemed seditious in an empire bound together by rituals honouring many gods and the divine majesty of the emperor. While persecution was not constant, it was often brutal. Christians were blamed for disasters, accused of atheism for refusing pagan rites, and subjected to mob violence or imperial decree. The Great Persecution under Diocletian at the start of the fourth century sought to extinguish the faith by burning scriptures, destroying churches, and compelling sacrifices to Roman gods.

Constantine

It was into this context that Constantine rose. In AD 312, before the Battle of the Milvian Bridge, he is said to have seen a vision of the cross with the words “In this sign, conquer.” Whether miracle or strategy, Constantine ordered his soldiers to march under the Christian symbol and secured a decisive victory. The following year, he and Licinius agreed to the Edict of Milan, granting all citizens the freedom to worship as they chose.

For Christians, the decree was liberation: confiscated property was restored, bishops emerged into public life, and the church began to build openly. For the empire, it marked the first legal recognition that matters of conscience should not be punished by the state.

The new freedom allowed Christianity to grow rapidly. Wealth and influence flowed into the church, and Christian leaders became voices in imperial politics. Yet Rome still remained religiously diverse. Pagan temples thrived, mystery cults endured, and even emperors hedged their bets between the old gods and the new faith. This pluralism ended with Theodosius I. In AD 380, with the Edict of Thessalonica, he declared Nicene Christianity the sole official religion of the empire. Pagan sacrifices were banned, heretical sects were branded illegal, and temples began to close.

Where Constantine had offered space for conscience, Theodosius fused church and state. Rome’s identity was now Christian. The shift ensured that Western law, culture, and philosophy would be shaped by Christian ethics: the dignity of every soul, the call to charity, and the rejection of cruelty as spectacle.

Slavery softened, gladiatorial games dwindled, and compassion became a civic virtue. Yet the fusion also carried a cost. The machinery of state could now enforce orthodoxy. Those outside the accepted creed, pagans, heretics, or Jews, could find themselves once again on the margins, this time in the shadow of a Christian empire.

Paradox

The twin edicts left a paradoxical inheritance. Milan planted the seed of freedom of conscience: the principle that faith should not be coerced, and that the state has a duty to permit diverse worship. Thessalonica, however, bound the empire to one creed, creating Christendom and shaping Europe’s identity for a millennium.

The tension between liberty of belief and enforced orthodoxy would echo through the Reformation, the Enlightenment, and into modern debates about the separation of church and state.Yet both edicts together made Christianity a world-shaping force. Freed by Constantine, the faith gained room to develop its theology, institutions, and cultural influence. Empowered by Theodosius, it became the central moral framework of Europe. Cathedrals, universities, hospitals, and a language of human dignity all trace their roots to this new status. The West’s moral imagination, from Augustine to Aquinas to Locke, unfolded in a world where Christianity was no longer hunted but enthroned.