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.