Constantine the Great
The emperor who converted Rome to Christianity and refounded its capital at Constantinople, reshaping Europe and the Church.
Constantine did two things that outlasted Rome itself: he made the empire Christian, and he shifted its center east to a city that still carries a version of his name. Born around 272 CE, the son of a Roman officer and a woman of humble origins named Helena, he fought his way to sole power through a generation of civil wars. Proclaimed emperor by his soldiers at York in 306, he took nearly twenty years to eliminate every rival and rule alone. By the time he died in 337 he had turned a hunted sect into the favored faith of the Roman state and bent the course of European history for good.
The vision at the bridge
In 312 CE Constantine marched on Rome to unseat his rival Maxentius. According to Christian writers, before the fighting he saw a sign in the sky, a cross of light with the words in this sign you will conquer, and ordered his soldiers to mark the symbol on their shields. At the Milvian Bridge over the Tiber, Maxentius's army broke and Maxentius himself drowned in the river. Constantine took the city. Whether or not he truly believed, he now credited the Christian God with his victory, and he acted on that credit quickly.
Legalizing a faith
In 313 CE Constantine and his co-emperor Licinius issued what history calls the Edict of Milan, ending official persecution and granting Christians the right to worship openly and reclaim confiscated property. A decade later, having beaten Licinius to rule alone, he inserted himself into the church's own quarrels. In 325 he summoned bishops from across the empire to the Council of Nicaea to settle a bitter dispute over the nature of Christ. It was the first time an emperor had presided over a council of the whole church. The argument pitted a priest named Arius, who held that Christ was created and lesser than God the Father, against those who insisted he was fully divine. Nicaea ruled against Arius and produced the creed that still defines mainstream Christianity.
A new Rome
Constantine's other monument was a city. In 330 CE he refounded the Greek town of Byzantium as Constantinople, a Christian capital astride the straits between Europe and Asia, walled, wealthy, and placed to command the trade and grain of the east. The old Rome faded; the new one thrived. He himself was baptized only on his deathbed in 337, a common practice then, having ruled for three decades as Christianity's patron rather than an ordinary believer. When the western empire collapsed in the fifth century, Constantinople carried on as capital of what we call the Byzantine Empire for another thousand years, until it fell to the Ottomans in 1453. One emperor's bet on a frontier city and a hunted faith reshaped the map and the soul of Europe.