The answer is Constantinople.
In 1453, Sultan Mehmed II, "The Conqueror" of the Ottoman Empire, attacked and conquered the capital's city of Roman/Byzantine Empire: Constantinople. One of the first things he did was to choose the city as his new capital, an Islamic one. He also turned Hagia Sophia (the main Greek cathedral) into a Turkish mosque, as well as many others, he initiated reconstruction projects for Constantinople and took several actions to re-populate it.
