Leo III (Leo the Isaurian or Leo the Syrian), c.680–741, Byzantine emperor (717–41). He was probably born in N Syria (rather than in Isauria, as once thought). He held diplomatic and military posts before he deposed and succeeded Theodosius III. His accession ended the anarchy into which the empire had fallen since the reign of Justinian II. Leo defended Constantinople against the last Arab siege (717–18), and although he had to contend with Arab attacks in Asia Minor, he succeeded in ending serious Arab threats for nearly two centuries and reorganized the military provinces ( themes ) of the empire for greater efficiency. His civil code, the Ecloga, written in Greek rather than in Latin, was a practical handbook that had considerable influence in Byzantium. He is also credited with issuing military, maritime, and rural codes. Leo's attack (726) on devotion to holy images began the long struggle over iconoclasm. Riots and rebellions broke out in Greece, while Byzantine rule in Italy (the exarchate of Ravenna and the Pentapolis of Rimini, Ancona, Fano, Pesaro, and Senigallia) began to crumble. The popes Gregory II and Gregory III opposed Leo's iconoclasm and successfully defied his armed expeditions, thus virtually ending Byzantine suzerainty over Rome. Nevertheless, Leo left a revitalized empire to his son, Constantine V. The Isaurian, or Syrian, dynasty, which he founded, ruled the Byzantine Empire until 802.
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