Battle of the Rishki PassStara Planina
Between 755 and 775, the Byzantine emperor Constantine V organised nine campaigns to eliminate Bulgaria and although he managed to defeat the Bulgarians several times, he never achieved his goal. In 759, the emperor led an army towards Bulgaria, but Khan Vinekh had enough time to bar several mountain passes. When the Byzantines reached the Rishki Pass they were ambushed and completely defeated. The Byzantine historian Theophanes the Confessor wrote that the Bulgarians killed the strategos of Thrace Leo, the commander of Drama, and many soldiers.
Khan Vinekh did not take the favourable opportunity to advance on enemy territory and sued for peace. This act was very unpopular among the nobles and the Khan was murdered in 761.