Grand Bazar, Istanbul, Turkey. Istanbul is the largest city in Turkey, constituting the country’s economic, cultural, and historical heart. Its commercial and historical centre lies in the European part of Eurasia, while about a third of its population lives in the Asian part. With a population of 14.1 million, the city forms the largest urban agglomeration in Europe as well as the largest in the Middle East, and the sixth-largest city proper in the world. Istanbul is a transcontinental city, straddling the Bosphorus strait in northwestern Turkey between the Sea of Marmara and the Black Sea.