Of Constantine’s early years, we know only that he was born in Illyria, a region in the Balkans. His father, Constantius Chlorus, was already a Roman official on the rise. Helena, the daughter of an innkeeper and Constantius’s wife, gave birth to Constantine around A.D. 280 in Naissus, just south of the Danube. By the time Constantine was 31, he was in line to become emperor of the western empire—and more.

In the spring of 311, with 40,000 soldiers behind him, Constantine rode toward Rome to confront an enemy whose numbers were four times his own. Maxentius, vying for supremacy in the West, waited in Rome with his Italian troops and the elite Praetorian Guard, confident no one could successfully invade the city. But Constantine’s army was already overwhelming his foes in Italy as he marched toward the capital.

Maxentius turned to pagan oracles, finding a prophecy that the “enemy of the Romans” would perish. But Constantine was still miles away. So, bolstered by the prophecy, Maxentius left the city to meet his foe.

Meanwhile, Constantine saw a vision in the afternoon sky: a bright cross with the words By this sign conquer. As the story goes, Christ himself told Constantine in a dream to take the cross into battle as his standard.

Though accounts vary, Constantine apparently believed the omen to be a word from God. When he awoke early the next morning, the young commander obeyed the message and ordered his soldiers to mark their shields with the now famous Chi-Rho.

Maxentius’s troops fled in disarray toward the surging Tiber. The would-be emperor attempted to escape over the wooden bridge erected to span the stream, but his own army-turned-mob, pressing through the narrow passage, forced him into the river, where he drowned by the weight of his armor.

Constantine entered Rome the undisputed ruler of the West, the first Roman emperor with a cross in his diadem.

Once supreme in the West, Constantine met Licinius, the ruler of the Balkan provinces, and issued the famous Edict of Milan that gave Christians freedom of worship and directed the governors to restore all the property seized during the severe Diocletian persecution.

Eusebius in his Church History recorded the Christian jubilation: “The whole human race was freed from the oppression of the tyrants. We especially, who had fixed our hopes upon the Christ of God, had gladness unspeakable.”

Constantine’s faith was still imprecise, but few questioned its authenticity. In 314 Constantine sent a message to the assembled bishops at the Council of Arles. He wrote about how God does not allow people “to wander in the shadows” but reveals to them salvation: “I have experienced this in others and in myself, for I walked not in the way of righteousness. … But the Almighty God, who sits in the court of heaven, granted what I did not deserve.”