History remembers constantine's victory at the battle of the Milvian Bridge. In 312 Constantine invaded Italy. Since his accession in 306 at York, the emperor had been residing primarily at Trier and campaigning on the Rhine frontier. He commanded a large army, most of it stationed in northern Gaul and Britain. For his invasion he took only a modest expeditionary force. In Italy the emperor Maxentius commanded another substantial army. To guard against an attack from the east by Licinius, yet another rival emperor who controlled the Balkans, Maxentius had moved troops to garrison Verona at the foot of the eastern Alps in northern Italy. Constantine and his army meanwhile crossed the western Alps at Susa and captured Turin and Milan as they advanced down the Po River valley. After a hard siege, they also captured Verona.

Constantine and his army next marched south on the Flaminian Way through central Italy toward Rome. Although in initial skirmishes Maxentius' troops prevailed, he himself remained inside the capital's massive wall. Constantine's soldiers then approached the Milvian Bridge, which carried the Flaminian Way across the Tiber River about two miles north of the wall. Maxentius' army crossed to meet them, and Maxentius himself joined his troops a bit later. At that point, or perhaps already earlier in anticipation of the invasion, his soldiers cut the permanent bridge and replaced it with a temporary pontoon bridge. But after they were routed in battle, their attempt to isolate the city turned into a bottleneck.