Janissaries
By 1826, the once elite corps of Janissaries, who were descended from Christian children (but by this time also included large numbers of Turkish conscripts) that were once collected in the Devshirme system and forced to become soldier-slaves,(but the system was corrupted later) were almost universally hated throughout Turkey because they had become a hereditary caste of corrupt Turkish soldiers. When they noticed that the sultan Mahmud II was forming a new army and hiring European gunners, they mutinied, but the Sipahis forced them to retreat to their barracks in the city of Thessaloniki. In the ensuing fight, the Janissary barracks were set in flames by artillery fire resulting in a massive number of casualties. Survivors were either exiled or executed and their possessions confiscated by the Sultan.
Read more about this topic: Massacres During The Greek Revolution