Constantinople (modern-day Istanbul) was the center of the Byzantine Empire. Founded by the Roman Emperor Constantine the Great in 330 AD, it was a critical political, economic, and cultural hub that served as the capital of the empire for over a thousand years. Its strategic location at the crossroads of Europe and Asia allowed for flourishing trade and cultural exchange, contributing to its prosperity. The city was renowned for its impressive architecture, including the Hagia Sophia, and played a vital role in the spread of Christianity and the preservation of Greek and Roman knowledge after the fall of the Western Roman Empire.