Istanbul, the largest city in Turkey, was the capital of the Byzantine and Ottoman empires. The Bosphorus straits divides the city into a part that sits on the European continent, and a larger part on the continent of Asia. The militarily and economically strategic position of the city, on the western portion of the Silk Road, and on the shipping route between the Aegean and Black Seas, has kept it cosmopolitan and prosperous since its foundation 660 BCE, when it was called Byzantium. In 330 it became Constantinople, the capital of the Roman Empire, named for Emperor Constantine the Great. The Ottomans conquered the city in 1453/857 AH and renamed the city Istanbul. It served as their capital until Ankara became the capital of the modern nation of Turkey.