Sack of Thessalonica (1185)

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.

Siege
David Komnenos, the governor, had failed to prepare for the siege and banned defenders from disrupting Norman siege works, hindering the city's defense.The Byzantine relief armies failed to coordinate their efforts, and only two forces, under Theodore Choumnos and John Maurozomes, actually came to the city's aid. In the event, the Normans undermined the city's eastern wall, opening a breach through which they entered the city. They slaughtered the defenders and proceeded to sack the city. The conquest degenerated quickly into a full-scale massacre of the city's inhabitants, with estimates suggesting that around 7,000 to 8,000 corpses were found afterwards. The siege is extensively chronicled by the city's archbishop, Eustathius of Thessalonica, who was present in the city during and after the siege.

Aftermath
The Normans occupied Thessalonica until mid-November, when, following their defeat at the Battle of Demetritzes, they evacuated it. After emperor Andronikos Komnenos's massacre of the Latins in Constantinople in 1182, the massacre of the Thessalonians deepened the rift between the Western Christianity and Eastern Christianity. It also directly led to the deposition and execution of the unpopular Emperor Andronikos and the rise to the throne of Isaac II Angelos.