The battle that led to the down fall of is known as "The siege of Constantinople". Constantinople was the capital city of the Byzantine Empire and one it was one of the most heavily fortified cities in the world in 1453. This battle after ten centuries of wars, defeats, and victories marked the end for the Byzantine Empire when Constantinople fell to the Ottoman Turks. It is said that Constantinople held out only because of its supposedly impregnable walls. The city was finally captured as the Ottoman Turks poured into the city through one of the gates that was forced (some claimed that it had been unlocked).
