In the early years of the 4th century A. D., the warrior Constantine aids his father, Emperor Constantius Chlorus, in fighting the barbarians and is summoned to receive honors in Rome. En route to the city with his friend Hadrian, a centurion, he is ambushed by the soldiers of Maxentius, his political rival, who shifts the blame for the attack to the Christians. After leaving the wounded Hadrian in the care of Livia, a Christian maiden, Constantine arrives in Rome. Livia is imprisoned for her beliefs but is released through the intervention of Constantine, who is accused of treachery and forced to flee the city, leaving behind his betrothed, Fausta, Maxentius' sister. Subsequently, Constantius reveals before his death that Constantine's mother, Helena, is also a Christian. Constantine is acclaimed Emperor of the West; and he announces a position of toleration towards the Christians. He weds Fausta, but her father, Maximian, urged by Maxentius, attempts to assassinate him and commits suicide when the plot fails. Maxentius becomes ruler of Rome, continues the cruel persecution of the Christians, and has Livia tortured and killed. Fausta travels to Rome to sway him, but he holds her prisoner and conspires to attack Constantine's forces in Gaul. Encouraged by a vision of the cross bearing the inscription, "By This Sign Conquer," Constantine defeats his enemies, rescues Fausta and his mother, and assures freedom of worship to the Christians.