The Topkapı Palace is a large palace in Istanbul, Turkey, that was the primary residence of the Ottoman Sultans for approximately 400 years (1465-1856) of their 624-year reign. Before you enter the Imperial Gate of Topkapı, take a look at the ornate structure in the cobbled square near the gate. This is the Fountain of Sultan Ahmet III, built in 1728 by the sultan who loved and promoted tulips so much that his reign was dubbed the 'Tulip Era'.