The Occupation of Constantinople took place in accordance with the Armistice of Mudros, ending the Ottoman participation in World War I. The occupation had two stages: the initial occupation took place from 13 November 1918 to 16 March 1920; from 16 March 1920 – Treaty of Sèvres. The year 1918 saw the first time Constantinople had changed hands since the Ottoman Turks conquered the Byzantine capital in 1453. An Allied military administration was set up early in December 1918. Hagia Sophia was converted back into a cathedral by the Allied administration, and the building was returned temporarily to the Greek Orthodox Ecumenical Patriarch.