In the eith quarter of the 8th century Bulgaria overcame the internal political crisis after the end of the rule of the Dulo. The khans Telerig and Kardam managed to consolidate the central authority and put an end of the quarrels among the nobility. The Bulgarians finally had the opportunity to intensify their campaigns in Macedonia and annex the region and its Slavic population to their state. In 789 they penetrated deep into the valley of the Struma river and heavily defeated the Byzantines, killing the strategos of Thrace Filites. In order to distract the Bulgarian attention from Macedonia, the Byzantine emperor Constantine VI started a campaign in northern Thrace in April 791. The armies met near the fortress of Provat (20 km east of Odrin) and the Byzantines were forced to retreat bu