Istanbul is a world city.
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 one of the world 's most populous cities and ranks as the world 's 7th-largest city proper and the largest European city . Approximately foreign visitors arrived in Istanbul in 2015 , five years after it was named a European Capital of Culture , making the city the world 's fifth most popular tourist destination . Considered a global city , Istanbul has one of the fastest-growing metropolitan economies in the world .