born 718, Constantinople
died Sept. 14, 775
Byzantine emperor (741–75).
The son of Leo III , he ruled with his father from 720. He spent his life defeating Arab and Bulgar threats to the empire and was unable to prevent the Lombards from taking Ravenna (751), thus ending Byzantine influence in northern and central Italy. A strong iconoclast (see iconoclasm ), he persecuted monks who disagreed with his position. He died in the Balkans on a military campaign against the Bulgarian kingdom.