Battle of the Milvian Bridge

Battle of the Milvian Bridge

The Battle of the Milvian Bridge on October 28, 312, took place just north of the Tiber River, about a mile and a half north of Rome. It confirmed Constantine as augustus (emperor) of the western portion of the Roman Empire. It also led to his becoming the first Christian leader of Rome.

For most of the third century the Roman Empire had experienced considerable chaos, including a rapid succession of emperors. Diocletian, who became emperor in 284, temporarily halted the decay. He also concluded that the empire was too vast to be ruled effectively by one man, so he instituted a tetrarchy, or rule by four men. He installed Maximian in the west, while Diocletian himself ruled in the east. Each held the title of augustus, and each appointed a subordinate to assist in ruling his half of the empire. These men—Galerius in the east and Constantius in the west—had the title of caesar. On the death or retirement of the augustus, the caesar was to succeed him and then name a caesar in his turn. This system was supposed to provide both an orderly transition to power and a training period for the most powerful position in the empire.

In 305 Diocletian retired and persuaded Maximian to do the same, whereupon Galerius and Constantius received the title of augustus. They named as caesars Flavius Severus in the west and Maximinus Daia in the east. These actions, however, angered two people who thought that position should be theirs: Constantine, the son of Constantius, and Marcus Aurelius Valerius Maxentius, son of Maximian.

In 306 Constantius died. His legions in Britain and Gaul proclaimed Constantine as augustus, although Constantine declined the title. Constantine was duly confirmed as caesar, but Severus became augustus in the west. The legions in Italy, however, refused to recognize Severus, proclaiming Maxentius as augustus. This led to civil war in the west during 306–307, ending with the execution of Severus and the proclamation of Maxentius as augustus. Maxentius acceded to his father Maximian, however, who came out of retirement and reclaimed the throne.

Galerius, in the eastern empire, refused to recognize either Constantine or Maximian as augustus. Galerius named one of his generals, Licianus Licinius, to replace Severus and invaded the western empire to enforce this decision. If all this was not already sufficiently complicated, Maxentius then forced his father from power again and assumed the title of western augustus. Galerius’s nephew Maximinus Daia also claimed the title.

To settle the issue, Diocletian called a conference in 308 at Carnuntum (presentday Hainburg, Austria). It confirmed all the claimants, except Maximian, in the title of augustus and gave each a portion of the empire to administer. This arrangement lasted only two years. In 310 Maximian fled from his son to Constantine’s court in Gaul. There Maximian intrigued to overthrow Constantine but was taken prisoner and forced to commit suicide. In 311 Galerius died, leaving four augusti: Constantine in Gaul, Maxentius in Italy, Licinius in the Balkans, and Maximinus Daia in the east.

The tyrannical Maxentius, convinced that Constantine was plotting against him, prepared for an invasion of Gaul. Learning of this, Constantine decided to strike first. Although he commanded some 100,000 men, Constantine was obliged to leave the majority of them to protect the frontiers. Constantine did conclude a pact with Licinius in the east, however, that included the pledge of the marriage of Constantine’s sister to Licinius in return for the latter’s neutrality.

With about 40,000 men Constantine moved swiftly through the Alps into northern Italy, where he won hard-fought battles against Maxentius’s legions at Susa, Turin, Milan, and Verona. As Constantine moved south his support increased, the result of both volunteers from the countryside and defections from Maxentius’s legions. By the time Constantine arrived just north of Rome he probably commanded about 50,000 men, while Maxentius had some 75,000 men. Maxentius sallied from Rome, positioning his men on the plain across the Tiber River near the village of Saxa Rubra.

On October 27 the day before the climactic battle, Constantine allegedly saw a sign in the sky that he and those around him interpreted as representing the Christian god. A story has it that during the night Constantine experienced a dream in which a voice told him to order his men to place the Greek letters chi and rho (the sign of Christ) on their shields, assuring him, “In this sign you will conquer.” In any case, Constantine ordered the symbols scratched into the shields prior to the battle. There were a number of Christians in Constantine’s army, and Eusebius, later bishop of Caesarea in Palestine, related that Constantine later told him that he had vowed before the battle to convert to that faith if he triumphed.

There are few details of the battle, which took place just north of the Tiber. Apparently both Constantine and Maxentius placed their infantry in the center and their cavalry on the flanks. The decisive point came when Constantine led a charge by one of his cavalry wings. Maxentius was utterly defeated. Only the Milvian Bridge was open as an escape route back to Rome, and not all the men could get across it in time. Maxentius and many of his legionnaires drowned in the Tiber. His body, clad in armor, was found the next day.

Following the battle, the Roman Senate recognized Constantine as sole augustus in the west. Constantine duly converted to Christianity, an act that encouraged many of his entourage to do the same. In 313 Constantine met with Licinius at Milan, and the two announced the Edict of Milan that pledged religious tolerance in the empire, to include Christianity. Constantine then fought hostile Germanic tribes while Licinius waged war against Maximinus Daia, defeating him.

Constantine and Licinius were soon quarreling, and in 323 Constantine defeated him. Licinius was executed the next year. In 325 Constantine called the Council of Nicea to define Christian doctrine. It declared some Christian beliefs heretical and blamed the Jews for Christ’s death, setting in motion a series of pogroms. Christians now persecuted other religions as Christianity once had been persecuted, and Christianity gradually became the dominant religion of the Roman Empire. Constantine, however, soon founded the city of Constantinople, setting up the formal division of the Roman Empire. The eastern portion, known as the Later Roman Empire or the Byzantine Empire, lasted until 1453.


Barnes, Timothy D. Constantine and Eusebius. Cambridge: Harvard University Press, 1981.

Cameron, Averil, and Stuart G. Hall. Eusebius: Life of Constantine. Oxford, UK: Clarendon, 1999.

Durant, Will. Caesar and Christ, Vol. 3, The Story of Civilization. New York: Simon and Schuster, 1944.

Ridley, Ronald T., ed. and trans. Zosimus: New History. Canberra: Australian Association for Byzantine Studies, 1982.