Istanbul (Turkish: Istanbul, historically known as Byzantium and Constantinople; see the names of Istanbul) is the largest city in Turkey and 5th largest city proper in the world with a population of 15 million, also making it the second largest metropolitan area in Europe by population, and the largest metropolitan city proper.
Istanbul is also a megacity, as well as the cultural, economic, and financial centre of Turkey. The city covers 39 districts of the Istanbul province. It is located on the Bosphorus Strait and encompasses the natural harbour known as the Golden Horn, in the northwest of the country. It extends both on the European (Thrace) and on the Asian (Anatolia) sides of the Bosphorus, and is thereby the only metropolis in the world that is situated on two continents.
In its long history, Istanbul has served as the capital city of the Roman Empire (330–395), the Eastern 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. Historic areas of Istanbul were added to the UNESCO World Heritage List in 1985.