Constantine won a decisive victory at the Milvian Bridge on 28 October 312, defeating his rival Maxentius for control of Rome and the western empire1. Christian writers said the battle began with a sign in the sky2, and it set Constantine on the path that would carry Christianity to the throne of the Caesars.
On a single day in October AD 312, two Roman emperors fought for the city of Rome, and the winner changed the course of Western history. The battle at the Milvian Bridge was not the largest Rome ever saw, but few have echoed longer. It decided who would rule the western empire, and, if the Christian writers are to be believed, it began with a sign in the sky that would carry a persecuted faith to the throne of the Caesars.
Two Emperors, One Rome
By 312 the Roman world was split among rival rulers, and two of them were closing on a collision. Constantine marched into Italy from the north with a battle-hardened army, beating Maxentius's forces in a string of victories as he drove toward the capital. Maxentius held Rome itself, with strong walls and a larger army, and at first meant to sit tight behind the defences. Instead, trusting to omens and to the crowds in the city3, he chose to march out and meet Constantine in the open beyond the Tiber.
The Sign in the Sky
It is here that the most famous story in the battle belongs. According to Christian writers, Constantine saw a sign of the cross, or the Chi-Rho monogram of Christ, together with the promise that in this sign he would conquer. He ordered the symbol painted on his soldiers' shields before the fight.3 Whatever a modern reader makes of the vision, Constantine went into battle under a new emblem, and he would build the rest of his reign on the victory that followed.
Disaster at the River
The fighting went against Maxentius almost from the start. Constantine's cavalry broke his flanks and his line began to give way, and the retreat quickly turned into a rout back toward the single crossing of the Tiber. The old stone Milvian Bridge had been partly cut3, and Maxentius's men crowded onto a makeshift bridge of boats.2 Under the press of the fleeing army it gave way. Thrown into the water in his armour, Maxentius drowned along with many of his soldiers, and his body was later pulled from the river.4
The Cross Comes to Power
The victory made Constantine master of the western empire, and in time of the whole Roman world. He threw his support behind Christianity, and in 313 the Edict of Milan granted the faith toleration across the empire5, ending the age of persecution. Within a few generations Christianity would become the empire's dominant religion. For that reason the Milvian Bridge is remembered less for its scale than for its consequences, one of the true turning points of the ancient world. See how Rome's armies were built to fight in how the Roman legion worked, revisit the earlier struggle for Rome at Actium, or check the terms in our military history glossary.
