Reign of Leo IVİstanbul, Turkey
When Constantine V died in September 775, while campaigning against the Bulgarians, Leo IV the Khazar became senior emperor on 14 September 775. In 778 Leo raided Abbasid Syria, decisively defeating the Abbasid army outside of Germanicia. Leo died on 8 September 780, of tuberculosis. He was succeeded by his underage son Constantine VI, with Irene serving as regent.