Istanbul is the major city located on both sides of the Bosporus, spanning Europe and Asia. Its European and Asian districts are separated by the strait, which links the Black Sea with the Sea of Marmara.
The city was founded as Byzantium, became Constantinople under the Roman and Byzantine empires, and was renamed Istanbul in common usage after the Ottoman conquest. It served as the capital of the Byzantine and Ottoman empires, although it is not the capital of modern Turkey; that role belongs to Ankara.
Istanbul’s geographic position made it a major centre of trade, politics, and culture. The Bosporus is a natural waterway, while the Golden Horn is a separate inlet on the city’s European side.