Istanbul, 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 between the Sea of Marmara and the Black Sea. Its commercial and historical center lies on the European side and about a third of its population lives on the Asian side.
The city is the administrative center of the Istanbul Metropolitan Municipality, both hosting a population of around 15 million residents. Istanbul is one of the world's most populous cities and ranks as the world's 4th-largest city proper and the largest European city. Istanbul is viewed as a bridge between the East and West.
Founded under the name of Byzantion on the Sarayburnu promontory around 660 BCE, the city grew in size and influence, having become one of the most important cities in history. After its reestablishment as Constantinople in 330 CE, it served as an imperial capital for almost 16 centuries, during the Roman/Byzantine, the Latin, and the Ottoman empires.