The Seven-Towered Castle. The fortress was an internal ring fortification located behind the Golden Gate of the Theodosian Wall and protected Constantinople from enemies who could break through the Golden Gate. The history of the fortress goes back more than 1,600 years. Construction began in 413 under the Roman Emperor Theodosius II and was completed in 439. After the conquest of Constantinople by the Ottomans in 1458, Sultan Mehmed II Fatih ordered three more towers to be added to the four towers of the Theodosian Walls, thus making the number of towers seven and significantly strengthening the city’s defenses. In the 1830s, Yedikule ceased to be used as a prison, the barracks were dismantled, and a school was built in their place. In 1895, the complex received the status of a museum.