Istanbul is a town.
Istanbul ( [ ˌɪstænˈbʊl ] , [ - ˈbuːl ] or [ - stɑːn - ] İstanbul [ isˈtɑnbuɫ ] ) , historically known as Constantinople and Byzantium , is the most populous city in Turkey and the country 's economic , cultural , and historic center . Istanbul is a transcontinental city in Eurasia , straddling the Bosphorus strait ( which separates Europe and Asia ) between the Sea of Marmara and the Black Sea . Founded under the name of Byzantion on the Sarayburnu promontory around 660 BCE , the city developed to become one of the most significant in history . Considered a global city , Istanbul has one of the fastest-growing metropolitan economies in the world .