Constantinople (kŏn´stăn´tĬnō´pəl), former capital of the Byzantine Empire and of the Ottoman Empire, since 1930 officially called İstanbul (for location and description, see İstanbul). It was founded (AD 330) at ancient Byzantium as the new capital of the Roman Empire by Constantine I, after whom it was named. The largest and most splendid European city of the Middle Ages, Constantinople shared the glories and vicissitudes of the Byzantine Empire, which in the end was reduced to the city and its environs. Although besieged innumerable times by various peoples, it was taken only three times—in 1204 by the army of the Fourth Crusade (see Crusades), in 1261 by Michael VIII, and in 1453 by the Ottoman Sultan Muhammad II. Defended by Greek fire, it was also well fortified. An early inner wall was erected by Constantine I, and the enlarged Constantinople was surrounded by a triple wall of fortifications, begun (5th cent.) by Theodosius II. Built on seven hills, the city on the Bosporus presented the appearance of an impregnable fortress enclosing a sea of magnificent palaces and gilded domes and towers. In the 10th cent., it had a cosmopolitan population of about 1 million. The Church of Hagia Sophia, the sacred palace of the emperors (a city in itself); the huge hippodrome, center of the popular life; and the Golden Gate, the chief entrance into the city; were among the largest of the scores of churches, public edifices, and monuments that lined the broad arcaded avenues and squares. Constantinople had a great wealth of artistic and literary treasures before it was sacked in 1204 and 1453. Virtually depopulated when it fell to the Ottoman Turks, the city recovered rapidly. The Ottoman sultans, whose court was called the Sublime Porte, embellished Constantinople with many beautiful mosques, palaces, monuments, fountains, baths, aqueducts, and other public buildings. After World War I the city was occupied (1918–23) by the Allies. In 1922 the last Ottoman sultan was deposed and Ankara became (1923) the new capital of Turkey.