Istanbul, Turkish İstanbul, formerly Constantinople, ancient Byzantium, largest city and principal seaport of Turkey. It was the capital of both the Byzantine Empire and the Ottoman Empire.
The old walled city of Istanbul stands on a triangular peninsula between Europe and Asia. Sometimes as a bridge, sometimes as a barrier, Istanbul for more than 2,500 years has stood between conflicting surges of religion, culture, and imperial power. For most of those years it was one of the most coveted cities in the world.