From 330 A.D. until World War II, two major world empires were centered in the region of today's Istanbul. What empires?

For over 1,600 years, the city we now call Istanbul served as the heart of two consecutive, world-shaping empires. The first began in 330 A.D. when Roman Emperor Constantine the Great (Review) relocated his capital from Rome to the ancient city of Byzantium, renaming it Constantinople. This marked the beginning of the Eastern Roman Empire, more commonly known as the Byzantine Empire. For more than a thousand years, Constantinople was a fortress city and a beacon of Orthodox Christianity, art, and commerce, bridging Europe and Asia.

The city's formidable walls were finally breached in 1453 by the forces of the Ottoman Sultan, Mehmed the Conqueror. This event marked the end of the Byzantine era and the beginning of the city's second great imperial chapter. As the new capital of the Ottoman Empire, Constantinople (eventually known as Istanbul) was transformed into the center of a vast Islamic caliphate. This powerful empire stretched across three continents at its height and endured for centuries, finally collapsing in the aftermath of World War I and leading to the formation of modern Turkey.