Istanbul (Turkish Istanbul), historically known as Byzantium and Constantinople (see Names of Istanbul for further information) is the largest city in Turkey and 2nd largest city proper in the world with a population of 13 million, also making it the largest metropolitan city proper in Europe and the second largest metropolitan area in Europe by population. 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.