The Metropolis of Nicomedia was an ecclesiastical territory (metropolis) of the Ecumenical Patriarchate of Constantinople in northwestern Asia Minor, modern Turkey. Christianity spread in Nicomedia already in the 1st century AD. Following the capture of the city by the Ottoman Turks in the early 14th century, the metropolitan see remained for a period vacant. The metropolis was re-established during the 15th century and remained active until the Greek-Turkish population exchange of 1922–1923.