Omortag

…upon Constantinople, and his son, Omortag, arranged a peace with the Byzantine Empire in order to protect the western frontiers of his Bulgar empire against the pressures exerted by Frankish expansion under Charlemagne and his successors. Since the death of the fifth caliph, Hārūn ar-Rashīd, had resulted in civil war…

…a treaty with Krum’s successor, Omortag, that determined the boundary between the two countries and provided a 30-year peace. In the ʿAbbāsid caliphate the troubles following the death of the caliph Hārūn al-Rashīd in 809 continued to provide the empire a respite from threats from the east.