Unlike the last dynasty, Caesar Tyrianus collaborated with the Senate, pledging to unite Rome against its new enemy. His predecessor had plunged the empire into bellum civile to try to maintain his hold on power but his failure allowed the empire to focus on the threat of Islam. On this front, Tyrian's first action was to appoint a new Generalissimus (most general commander of legions) and send him to lead the ten legions spread across the eastern provinces. When Caliph Umar invaded in 646 with a fleet that carried an army, his forces were repelled by this supreme commander and his men. With another great army defeated, the Caliphate would not be keen on continued conflict with Rome.