It remained so for nearly 500 years. At its height, Ottoman power surged through the Balkans and reached the walls of Vienna. It seemed as if all of Europe might fall. But Vienna held. And by the 17th century, the Ottomans entered a long, slow decline. The once proud Muslim state became the “Sick Man of Europe,” propped up by stronger Christian, European nations.

The centuries of impotence and humiliation culminated in the complete collapse of the Ottoman empire in the 1920s. Under the leadership of a charismatic nationalist named Mustafa Kemal Atatürk, the Caliphate was abolished and a republic was founded on a Western, secular model. Atatürk’s modern state was an explicit rejection of the Islamic theocratic system, and he needed a powerful symbol to drive this point home. Once again, the Hagia Sophia was pressed into service. In 1931, Islamic services were stopped. Three years later, it officially opened as a museum. A quintessential icon of the militant, Islamic past was now a symbol of modern Turkey.