Constantinople (modern-day Istanbul) was the center of the Byzantine Empire. It was founded by Emperor Constantine the Great in 330 AD, who made it the capital of the Byzantine Empire, which was the eastern continuation of the Roman Empire. Strategically located at the crossroads of Europe and Asia, Constantinople flourished as a hub of trade, culture, and politics for over a millennium. Its impressive architecture, including the Hagia Sophia, and fortified walls contributed to its reputation as a formidable metropolis. The city remained a center of Orthodox Christianity until it fell to the Ottoman Turks in 1453, marking the end of the Byzantine Empire.