Maxentius (Marcus Aurelius Valerius Maxentius)măksĕnˈshəs, d. 312, Roman emperor (306–12), son of Maximian. After Diocletian and Maximian had retired, the successor to Maximian, Constantius, died. The Romans, discontented with the shift of power away from Rome, supported Maxentius, who claimed the throne. His father came out of retirement to help him when Severus (d. 307) and Galerius came to force him to submission. Severus was compelled to surrender, and Galerius had to withdraw from Italy, while a fourth seeker for power, Constantine (Constantine I) was persuaded to recognize Maxentius. Maxentius and his father fell out, however, and Constantine turned against Maxentius, whom he defeated (312) in the battle of Milvian Bridge.