Battle of the Milvian Bridge (312): Constantine's Victory

The Battle of the Milvian Bridge was fought on 28 October AD 312 just north of Rome between two rival Roman emperors, Constantine and Maxentius. Constantine’s victory, after a rapid invasion of Italy from Gaul, made him master of the western Roman Empire. Because Christian writers linked it to a vision in which Constantine was told to fight under a Christian sign, the battle became one of the most famous turning points in the history of Christianity and of Europe.

Background: the end of the Tetrarchy

In 293 the emperor Diocletian had divided imperial power among four rulers, the Tetrarchy. When he and his colleague Maximian abdicated in 305, their junior partners Constantius and Galerius became senior emperors. The sons of Constantius and Maximian, Constantine and Maxentius, were passed over.

Neither accepted it. When Constantius died at York on 25 July 306, his troops proclaimed Constantine emperor. A few months later, on 28 October 306, Maxentius was proclaimed in Rome with the support of the Praetorian Guard and the city’s people, who resented losing their privileges and tax exemptions.

Maxentius held Italy and, for most of his reign, North Africa. He defeated two attempts to remove him: the emperor Severus invaded in 307, was deserted by his troops and later killed, and Galerius’s own invasion later that year ended in retreat. By 312 the empire had several rival rulers: Constantine in Gaul and Britain, Maxentius in Italy and Africa, Licinius in the Balkans and Maximinus Daia in the East.

Relations between Constantine and Maxentius broke down after the death of Maximian, Maxentius’s father, who had taken refuge with Constantine, rebelled against him and died at Massilia (Marseille) in 310. Maxentius presented himself as avenging his father, and Constantine allied himself with Licinius, betrothing his half-sister Constantia to him.

Constantine’s march on Italy

In the spring of 312 Constantine crossed the Alps, probably by the Mont Cenis pass, with an army drawn from his Rhine and Gallic forces. He left a large part of his troops behind to guard the Rhine frontier. Modern historians usually estimate his invading force at about 40,000 men, while the ancient historian Zosimus gives an implausible 98,000.

The campaign moved quickly. Constantine stormed Segusium (Susa), defeated a force including heavy armoured cavalry near Turin, and was welcomed into Milan. He then defeated Maxentius’s forces at Brescia and laid siege to Verona, where Maxentius’s praetorian prefect Ruricius Pompeianus was killed in battle. With northern Italy secured, Constantine advanced down the Via Flaminia towards Rome.

Maxentius’s choice

Maxentius had prepared for a siege. Rome was protected by the Aurelian Walls, which he had strengthened, and he had stored grain in the city. He had also cut the Milvian Bridge, the stone bridge that carried the Via Flaminia over the Tiber, to slow any attacker.

Yet in the end he chose to fight in the open. Lactantius says there were riots in Rome and that the crowd at the circus shouted that Constantine could not be beaten. Maxentius consulted the Sibylline Books, the ancient prophetic texts kept by priests in Rome, and was told that on that day the enemy of the Romans would perish. He took this as a promise of victory. The day chosen, 28 October, was the sixth anniversary of his accession, a date of good omen.

The vision of Constantine

The most famous part of the story concerns what Constantine saw before the battle. There are two main accounts, and they differ.

Lactantius, writing around 315, only a few years later, says that Constantine was told in a dream to mark the “heavenly sign of God” on his soldiers’ shields. The sign he describes appears to be a cross-like symbol with a looped top, or the Chi-Rho, the first two Greek letters of the name Christ (Χ and Ρ) placed over one another.

Eusebius of Caesarea, in his Life of Constantine written after the emperor’s death in 337, gives a fuller version that he says Constantine himself told him and swore to be true. During the march, at about midday, Constantine and his whole army saw a cross of light above the sun with the words “In this conquer” (in Greek, en toutoi nika). That night Christ appeared to him in a dream and told him to make a copy of the sign as a protection in battle. This became the labarum, a military standard topped by the Chi-Rho.

Historians have debated these accounts for centuries. Some suggest that Constantine saw a rare solar halo, an atmospheric effect that can produce rings and crosses of light around the sun. Others note that in 310 a pagan orator described Constantine seeing a vision of the god Apollo in Gaul, suggesting that he was already inclined to look for divine signs. What is clear is that from 312 onwards Constantine publicly credited the God of the Christians with his victory.

The battle

Maxentius’s army crossed the Tiber over a temporary bridge of boats built beside the damaged stone bridge and drew up on the northern bank. The two armies met on the plain near Saxa Rubra, a few kilometres north of the bridge along the Via Flaminia.

Maxentius’s troops were deployed with the river at their backs, a dangerous position that left little room to manoeuvre or retreat. Constantine’s cavalry charged and broke Maxentius’s cavalry on the wings, and his infantry then advanced. Many of Maxentius’s soldiers fled towards the river. Only the Praetorian Guard, who owed their existence to Maxentius, are said to have stood and fought, dying where they stood.

The retreat became a catastrophe. The pontoon bridge collapsed under the weight of the fleeing army, or was broken deliberately, and thousands were drowned in the Tiber. Maxentius himself was among them, pulled down by his armour. His body was recovered from the river the next day, and his head was cut off and carried on a spear when Constantine entered Rome. No reliable casualty figures exist.

Constantine in Rome

Constantine entered Rome on 29 October 312. He did not, as custom expected, climb the Capitol to sacrifice to Jupiter, a detail many historians see as significant. He disbanded the Praetorian Guard, which had made and unmade emperors for three centuries, and destroyed its camp. He also dissolved the imperial horse guard that had served Maxentius.

The Senate declared him the senior Augustus. Maxentius’s building projects, including the great basilica near the Forum, were completed in Constantine’s name, and a colossal statue of Constantine was placed inside it. Constantine also gave land for a great church at the Lateran, the first major imperial church foundation in Rome.

In 315 the Senate dedicated the Arch of Constantine beside the Colosseum to celebrate his victory over the “tyrant”. Its inscription says he won “by the inspiration of the divinity”, a phrase vague enough to suit both Christians and traditional worshippers.

Consequences

The battle settled the West. In February 313 Constantine met Licinius at Milan, where Licinius married Constantia, and the two rulers agreed the policy of religious toleration known as the Edict of Milan. Licinius then defeated Maximinus Daia and took the East.

The partnership did not last. Constantine and Licinius fought a first war around 316 and a decisive one in 324, which ended with Constantine as sole emperor. He founded Constantinople as a new imperial capital and summoned the Council of Nicaea in 325.

For Christianity, the battle marked the beginning of imperial patronage. Constantine gave the Church money, buildings and legal privileges, and bishops gained a public role. Over the following century Christianity went from a recently persecuted minority to the majority faith of the Roman world.

Myths and facts

Myth: Constantine converted to Christianity at the battle. His commitment grew over years. His coins continued to show the sun god Sol Invictus until the early 320s, and he was baptised only on his deathbed in 337.

Myth: Maxentius was a persecutor of Christians. Christian writers later cast him as a cruel tyrant, but he had actually ended the persecution in his territories and returned confiscated property to the Church in Rome around 311.

Myth: Constantine’s soldiers carried crosses. The sign described by the early sources was most likely the Chi-Rho or a similar monogram, not a plain cross, and only Eusebius describes a cross in the sky.

Fact: the phrase “In hoc signo vinces” is a later Latin form. Eusebius gives the words in Greek. The Latin version became famous in the Middle Ages and later appeared on coats of arms, coins and flags.

Timeline

• 306, 25 July: Constantine is proclaimed emperor at York.
• 306, 28 October: Maxentius is proclaimed emperor in Rome.
• 307: Invasions of Italy by Severus and Galerius fail.
• 310: Maximian dies at Massilia after a failed revolt against Constantine.
• 312, spring: Constantine crosses the Alps into Italy.
• 312, summer: Victories at Turin and Brescia; siege of Verona.
• 312, 28 October: Battle of the Milvian Bridge; Maxentius drowns.
• 312, 29 October: Constantine enters Rome.
• 313, February: Constantine and Licinius meet at Milan.
• 315, July: The Arch of Constantine is dedicated during his tenth anniversary celebrations.

Why it matters

The Battle of the Milvian Bridge gave Constantine control of Rome and the West and began the chain of events that made him sole emperor. Because he attributed his victory to the Christian God, it also marked the moment the Roman state began to favour Christianity. Few single afternoons have had such long-lasting consequences for the religion and culture of Europe.