Pope Leo IV

Pope Leo IV (died 17 July 855) was the bishop of Rome and leader of the Papal States from 10 April 847 to his death in 855. 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.

Source: Wikipedia — https://en.wikipedia.org/wiki/Pope_Leo_IV