Constantinople served as the capital of the Byzantine Empire. Founded as Byzantium, it was renamed Constantinople in honor of Emperor Constantine the Great in 330 AD. The city's strategic location at the crossroads of Europe and Asia made it a vital center for trade, culture, and politics. Constantinople was renowned for its impressive architecture, including the Hagia Sophia, and its formidable defensive walls, which helped protect it from invaders for centuries. The city played a crucial role in preserving and transmitting classical knowledge during the Middle Ages. Its fall to the Ottoman Empire in 1453 marked the end of the Byzantine Empire and a significant shift in world history.