Pope Leo IV

Leo IV became bishop of Rome on 10 April 847, inheriting a city scarred by Arab raids. He set to work repairing the damaged churches and then turned to prevention: he constructed the Leonine Wall around Vatican Hill, a defensive barrier meant to keep future attackers at bay. When Saracen forces threatened again by sea, he organized a league of Italian cities and led them to victory at the Battle of Ostia. He died on 17 July 855, having spent eight years shoring up both the physical and political defenses of Rome.