According to Lactantius, a Latin historian of North African origins saved from poverty by the Emperor Constantine the Great (r. 306–337), who made him tutor to his son Crispus, Constantine had dreamt of being ordered to put a "heavenly divine symbol" () on the shields of his soldiers. The description of the actual symbol chosen by Emperor Constantine the next morning, as reported by Lactantius, is not very clear: it closely resembles a Tau-Rho or a staurogram (), a similar Christian symbol. That very day Constantine's army fought the forces of Maxentius and won the Battle of the Milvian Bridge (312), outside Rome.