Istanbul is the 4th largest city in the world. Located on the Bosphorus Strait, Istanbul extends both on the European (Thrace) and on the Asian (Anatolia) side of the Bosphorus, and is thereby the only city situated on two continents.

Istanbul served as the capital city of the Roman Empire (330–395), the East Roman (Byzantine) Empire (395–1204 and 1261–1453), the Latin Empire (1204–1261), and the Ottoman Empire (1453–1922). The city was chosen as joint European Capital of Culture for 2010. — Wikipedia

… but the capital of Turkey is Ankara.

(photo: A painting on the wall of a cruise ship on the Bosphorus)