The city known for its historic significance as the capital of the Byzantine Empire is Constantinople, now called Istanbul, located in Turkey. Founded by the Roman Emperor Constantine the Great in 330 AD, it served as a critical center of commerce, culture, and religion for over a millennium. The city is famous for its rich history and architectural marvels, including the Hagia Sophia and Topkapi Palace. Its strategic location between Europe and Asia contributed to its significance in both the ancient and medieval worlds.