Istanbul is a town.
Istanbul . 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 . Istanbul is one of the world 's most populous cities and ranks as the world 's 7th-largest city proper and the largest European city . Considered a global city , Istanbul has one of the fastest-growing metropolitan economies in the world .