The largest city of Turkey, in the northwest part of the country on both sides of the Bosporus at its entrance into the Sea of Marmara. Founded c. 660 B.C. as Byzantium, it was renamed Constantinople in A.D. 330 by Constantine the Great, who made it the capital of the Eastern Roman, or Byzantine, Empire. The city was sacked by Crusaders in 1204 and taken by the Turks in 1453. Istanbul was chosen as the official name in 1930. Population: 8,800,000.