Battle in Thrace, 502

In 502, the Bulgars invaded Thrace and the western parts of the Balkan Peninsula. The attack met no resistance from the local population, which was poorly protected and unprepared to repel such an assault.
At the same time, the Byzantine Empire, ruled by Emperor Anastasius I, was at war with Persia. This conflict absorbed a substantial proportion of the empire's resources and army, weakening its northern and western frontier defences. The Bulgars thus exploited Byzantium's military difficulties and succeeded in penetrating its territory.

Although these attacks did not lead to permanent Bulgar settlement south of the Danube, they foreshadowed future large-scale conflicts in the Balkans.