Pope Leo IV (790 – 17 July 855) was the bishop of Rome and ruler of the Papal States from 10 April 847 to his death. He is remembered for repairing Roman churches that had been damaged during the Arab raid against Rome, and for building the Leonine Wall around Vatican Hill to protect the city. Pope Leo organized a league of Italian cities who fought and won the sea Battle of Ostia against the Saracens. Early career A Roman by birth, Leo received his early education at Rome in the monastery of St. Martin, near St. Peter's. He attracted the notice of Pope Gregory IV, who made him a subdeacon; and was created cardinal-priest of Santi Quattro Coronati by Pope Sergius II. Pontificate In April 847, Leo was unanimously chosen to succeed Sergius II. As the attack of the Saracens on Rome in 846 caused the people to fear for the safety of the city, he was consecrated on 10 April, 847 without waiting for the consent of the emperor. Saracen defenses He immediately began to repair the damage done to various churches of the city during the Arab raid against Rome. He restored and embellished the damaged Basilica of Saint Paul Outside the Walls and St. Peter's Basilica. The latter's altar again received its gold covering (after being stolen), which weighed 206 lb. and was studded with precious gems. Following the restoration of St. Peter's, Leo appealed to the Christian kingdoms to confront the Arab raiders. Leo also took precautions against further raids. He put the walls of the city into a thorough state of repair, entirely rebuilding fifteen of the great towers. He was the first to enclose the Vatican hill by a wall. Leo ordered a new line of walls encompassing the suburb on the right bank of the Tiber to be built, including St. Peter's Basilica, which had been undefended until this time. The district enclosed by the walls is still known as the Leonine City, and corresponds to the later rione of Borgo. To do this, he received money from the emperor, and help from all the cities and agricultural colonies (domus cultae) of the Duchy of Rome. The work took him four years to accomplish, and the newly fortified portion was called the Leonine City, after him. Battle of Ostia In 849, when a Saracen fleet from Sardinia approached Portus, Leo IV summoned