Sack of Thessalonica
1185 CE.
Shown on the map at 40.633°, 22.950°.
The sack of Thessalonica in 1185 by Normans of the Kingdom of Sicily was one of the worst disasters to befall the Byzantine Empire in the 12th century.
Text from the Wikipedia article Sack of Thessalonica (1185), licensed CC BY-SA 4.0.