Siege of Debeltos
812 CE.
Shown on the map at 42.387°, 27.284°.
The siege of Debeltos was fought between the Eastern Roman Empire and Bulgaria from May to June 812. The siege took place at the city of Debeltos in Thrace and resulted in a Bulgarian victory.
Text from the Wikipedia article Siege of Debeltos, licensed CC BY-SA 4.0.