The White tower of Thessaloniki is a monument and museum on the waterfront of the city of Thessaloniki in northern Greece. Originally constructed by the Ottomans to fortify the city's harbour, it became a notorious prison and scene of mass executions during the period of Ottoman rule. It was substantially remodeled and its exterior was whitewashed after Greece gained control of the city in 1912, turning the former "Tower of Blood" into the present-day White Tower. It has been adopted as the symbol of the city, and also as a symbol of Greek sovereignty over Macedonia.