The Tower was used by the Ottomans successively as a fort, garrison and a prison. In 1826, at the order of the Sultan Mahmud II, there was a massacre of the prisoners in the Tower. Owing to the "countless victims of Ottoman torturers and executioners", the tower acquired the name "Tower of Blood" or "Red Tower" (Turkish: Kanli Kule), which it kept until the end of the 19th century.
The Tower was for centuries part of the walls of the old city of Thessaloniki, and separated the Jewish quarter of the city from the cemeteries of the Muslims and Jews. The city walls were demolished in 1866. When Thessaloniki was annexed from the Ottoman Empire to the Greek State in 1912 during the First Balkan War, the tower was whitewashed as a symbolic gesture of cleansing, and acquired its present name. King George I of Greece was assassinated not far from the White Tower in March 1913.
The Tower is now a buff colour but has retained the name White Tower. It now stands on Thessaloniki's waterfront boulevard, Nikis (Victory) Street. It houses a museum dedicated to the history of Thessaloniki and is one of the city's leading tourist attractions. The Tower is under the administration of the Ephorate of Byzantine Antiquities of the Greek Ministry of Culture. wikipedia