Constructed between 1372 and1540 during the Ming Dynasty, Jiayuguan or Jiayu Pass 嘉峪關 marks the western end of the Ming-era Great Wall. Beyond this point lay the vast Gobi Desert and Central Asia, which the ancient Chinese considered the boundary of the civilized empire. The pass is located at the narrowest point of the western section of the Hexi Corridor, 6 km (3.7 mi) southwest of the city of Jiayuguan. Unlike the brick walls near Beijing, Jiayuguan Fort was primarily built using rammed earth (loess) layered inside heavy outer walls. The complex features inner and outer courtyards, watchtowers, barbicans, and a surrounding moat. A major conservation and reconstruction project in 2012-2017 results in the current form. From left to right (east to west) are three towers: Guanghua Gate 光化門, Rouyuan Gate 柔遠門, and Jiayuguan 嘉峪關 .