Leo III

(born c. 675, Germanicia, Commagene, Syria—died June 18, 742, Constantinople) Byzantine emperor (717–41), founder of the Isaurian dynasty. A high-ranking military commander, he seized the throne with the help of Arab armies who hoped to subjugate the Byzantine Empire. He then successfully defended Constantinople against the Arabs (717–718). Having crowned his son Constantine V coemperor (720), Leo used his son's marriage to cement an alliance with the Khazars. Victory over the Arabs at Akroïnos (740) was crucial in preventing their conquest of Asia Minor. Leo issued an important legal code, the Ecloga (726). His policy of iconoclasm (730), which banned the use of sacred images in churches, engendered a century of conflict within the empire and further strained relations with the pope in Rome.