Battle of the Milvian Bridge

Background

In the late third century the Roman emperor Diocletian divided the empire into four parts and established the Tetrarchy, a system in which two senior emperors (Augusti) and two junior emperors (Caesars) ruled jointly. This arrangement collapsed after his abdication. When Constantius, the Augustus of the West, died in Britain in 306, the army proclaimed his son Constantine emperor. In the same year Maxentius, son of the former emperor Maximian, seized power in Rome. The two men became rivals for supremacy over the Western Empire. At the time, Christians had only recently endured the Great Persecution, which began in 303.

Course of the Campaign

In 312 Constantine led his army out of Gaul and across the Alps. After defeating Maxentius's forces in succession at Turin, Verona, and elsewhere in northern Italy, he marched south toward Rome. Rather than hold out behind the city walls, Maxentius chose to cross the Tiber and give battle.

On October 28, 312, the two armies met near the Milvian Bridge north of Rome. Constantine's forces prevailed, and Maxentius's army was driven back toward the bridge, where Maxentius drowned in the Tiber. Ancient records report that a temporary pontoon bridge (a bridge made of boats lashed together), which Maxentius's side had laid across the river, collapsed. The following day Constantine entered Rome.

Two traditions describe how Constantine received a divine sign before the battle:

• Lactantius: He wrote that Constantine was instructed in a dream to mark a heavenly sign on his soldiers' shields. This sign is understood to be the Greek letters chi (Χ) and rho (Ρ), superimposed on each other to signify Christ.
• Eusebius of Caesarea: In his Life of Constantine, he wrote that the emperor saw in the sky a cross-shaped light together with the words "By this, conquer." Eusebius stated that he had heard this account directly from the emperor. The sign is said to have later been made into a military standard known as the labarum.

Outcome and Impact

Constantine became the sole ruler of the Western Empire. In 313, together with Licinius, emperor in the East, he adopted a policy granting freedom of religion, including Christianity. This policy is commonly called the "Edict of Milan." Thereafter the church recovered its property and received state support. Constantine became deeply involved in church affairs, convening the Council of Nicaea in 325, among other actions. The Arch of Constantine, erected in Rome in 315, bears an inscription stating that the victory was won "by the inspiration of the divinity." The arch, however, does not explicitly refer to the Christian God.

Assessment

The battle is commonly regarded as the turning point at which a persecuted Christianity became a religion under imperial protection. Interpretations, however, differ.

• The vision accounts: The two accounts differ in content and timing, and scholars are therefore divided over their historicity.
• The nature of the conversion: Constantine was baptized only in 337, shortly before his death. For this reason, debate has continued over whether his conversion reflected genuine faith or political calculation.
• The union of church and state: Many churches regard the changes that followed this event as a providential opening of the way for the spread of the gospel. By contrast, the Mennonites and others in the Anabaptist tradition view it critically as the beginning of the church's alliance with state power. A prominent example is the Mennonite theologian John Howard Yoder, who called it the "Constantinian shift." This debate is frequently invoked in discussions of the relationship between church and politics.