Byzantine–Bulgarian wars: Battle of Kleidion: Byzantine emperor Basil II inflicts a decisive defeat on the Bulgarian army, and his subsequent treatment of 15,000 prisoners reportedly causes Tsar Samuil of Bulgaria to die of a heart attack less than three months later, on October 6.

The Byzantine–Bulgarian wars were a series of conflicts fought between the Byzantine Empire and the Bulgarian Empire which began already in the late 5th century when the Bulgars defeated a 15.000 Roman army led by Magister Aristus. The Bulgars permanently conquered parts of the Balkan Peninsula…