"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. ...
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He is remembered for repairing Roman churches that had been damaged during Arab raids on Rome, and for building the Leonine Wall around Vatican Hill. Pope Leo organized a league of Italian cities who fought and won the sea Battle of Ostia against the Saracens." - (en.wikipedia.org 11.08.2021)