Titular sees are dioceses that no longer functionally exist, often because the territory was conquered by Muslims or because it is schismatic. The Greek–Turkish population exchange of 1923 also contributed to titular sees. The see of Maximianoupolis along with the town that shared its name was destroyed by the Bulgarians under Emperor Kaloyan in 1207; the town and the see were under the control of the Latin Empire, which took Constantinople during the Fourth Crusade in 1204.