It would be hard if not outright impossible to overstate the impact Roman Emperor Constantine I had on the history of Christianity, Rome, and Europe as a whole. Best known as Constantine the Great, the kind of moniker only earned by rulers who have distinguished themselves in battle and conquest, Constantine remains an influential and controversial figure to this day. He achieved enduring fame by being the first Roman emperor to personally convert to Christianity, and for his notorious Edict of Milan, the imperial decree which legalized the worship of Christ and promoted religious freedom throughout the empire.

Moreover, even though he is best remembered for his religious reforms and what his (mostly Christian) admirers described as his spiritual enlightenment, Constantine was also an able and effective ruler in his own right. Rising to power in a period of decline and confusion for the Roman Empire, he gave it a new and unexpected lease on life by repelling the repeated invasions of the Germanic tribes on the Northern and Eastern borders of the Roman domains, even going so far as to re-expand the frontier into parts of Trajan’s old conquest of Dacia (modern Romania), which had been abandoned as strategically untenable.

Rome’s civil wars and imperial crisis might have destroyed a weaker empire, and the fact that they did not demonstrated the resilience of Roman institutions and the very concept of the Imperium Romanum. Through Constantine and Christianity, that idea survived in various incarnations, and it would serve as a model for the Byzantine Empire, the Holy Roman Empire, the Napoleonic Empire, Germany, and even Russia. It persists to this day via the European Union, a powerful reminder that even as the continent has been home to countless ethnicities, cultures, and religions, Europe clings to the notion of the Pax Romana.