The Battle of the Milvian Bridge took place between the Roman Emperors Constantine I and Maxentius on 28 October 312. Constantine won the battle and started on the path that led him to end the Tetrarchy and become the sole ruler of the Roman Empire. Maxentius drowned in the Tiber during the battle.

According to chroniclers such as Eusebius of Caesarea and Lactantius, the battle marked the beginning of Constantine's conversion to Christianity. Lactantius recounts that Constantine and his soldiers had a vision that God promised victory if they daubed the sign of the cross on their shields. The Arch of Constantine, erected in celebration of the victory, certainly attributes Constantine's success to divine intervention; however, the monument does not display any overtly Christian symbolism.