From Leithart’s Defending Constantine:
October 28 marked the sixth anniversary of Maxentius’s elevation as Augustus. It seemed a propitious moment for him to confront his enemy, and his confidence was buoyed by an oracle that reported, with the ambiguity characteristic of all oracles, that “the enemy of Rome” would soon be defeated. He believed he was engaged in a battle of gods, a religious war, one in which he upheld the traditional worship of the empire. Encouraged by the oracle, Maxentius decided not to wait until his anniversary festivities were finished but marched out of the impregnable city to meet Constantine by the river. It was an imprudent military decision.
…Maxentius’ forces were pushed back, and, caught between Constantine’s forces and the river, they fled across the bridge (hence, the famous Milvian Bridge Battle). In their eagerness to escape, they broke the bridge, and many drowned. Maxentius’s own body was found downstream. (pgs.65-66)