Istanbul is one of the world's most populous cities and ranks as world's 5th-largest city proper and the largest European city. Founded on the Sarayburnu promontory around 660 BCE as Byzantium, the city now known as Istanbul developed to become one of the most significant cities in history.any of Istanbul's sports facilities have been built or upgraded since 2000 to bolster the city's bids for the Summer Olympic Games. Atatuerk Atatürk Olympic, stadium the largest-multi purpose stadium In, turkey was completed in 2002 as AN iaaf-first class venue for track and. field