By about 580, the Avar Khagan Bayan I had established supremacy over most of the Slavic, Bulgar and Germanic tribes living in Pannonia and the Carpathian Basin. When the Byzantine Empire was unable to pay subsidies or hire Avar mercenaries, the Avars raided their Balkan territories. According to Menander, Bayan commanded an army of 10,000 Kutrigur Bulgars and sacked Dalmatia in 568, effectively cutting the Byzantine terrestrial link with North Italy and Western Europe. By 582, the Avars had captured Sirmium, an important fort in Pannonia. When the Byzantines refused to increase the stipend amount as requested by Bayan's son and successor Bayan II (from 584), the Avars proceeded to capture Singidunum and Viminacium. They suffered setbacks, however, during Maurice's Balkan campaigns in the 590s.