Istanbul (Turkish: İstanbul, historically Byzantium and later Constantinople) is Turkey's most populous city, and its cultural and financial center. The city covers 25 districts of the Istanbul province. It is located at 41° N 29° E, on the Bosphorus strait, and encompasses the natural harbor known as the Golden Horn, in the northwest of the country. It extends both on the European (Thrace) and on the Asian (Anatolia) side of the Bosphorus, and is thereby the only metropolis in the world which is situated on two continents. In its long history, Istanbul (Constantinople) served as the capital city of the Roman Empire (330-395),