Constantinople had stood for more than a thousand years as the capital of the Eastern Roman Empire and the center of Eastern Christianity. In 1453, after a siege of many weeks, the city fell to the army of the Ottoman Sultan Mehmed II.
The great church of Hagia Sophia became a mosque. The Eastern Roman Empire, which had outlived the Western by nearly a thousand years, came to an end. The Orthodox Church entered a long period under Ottoman rule.
Scholars fleeing the city carried Greek manuscripts and learning into Western Europe, where they fed the Renaissance. And the center of Orthodox Christian life shifted northward — above all to Russia, which would come to call Moscow a 'third Rome.'