Tervel of Bulgaria, son of Asparukh, was the Khan at the beginning of the 8th century. In 705, Emperor Justinian II named him Caesar, the first foreigner to receive this title. Tervel played an important role in defeating the Arabs during the Siege of Constantinople in 717–718. During Krum’s reign in the early 9th century, Bulgarian territory doubled in size, spreading from the middle Danube to the Dnieper and from Odrin to the Tatra Mountains. His able and energetic rule brought law and order to Bulgaria and developed the rudiments of state organization.