The Topkapi Palace was the official and primary residence of the Ottoman Sultans for nearly 400 years of their 600-year reign,from 1465 to 1856. Initial construction of the palace began in 1459, ordered by Sultan Mehmed II, the conqueror of Byzantine Constantinople. Nowadays a major tourist attraction, the palace used to be a setting for state occasions and royal entertainments. Topkapi Palace is among those monuments belonging to the "Historic Areas of Istanbul", which became a UNESCO World Heritage Site in 1985.