Jiayuguan pass, also called Jiayu Pass, is the first pass at the west end of the Great Wall of China. The pass was built during the early Ming Dynasty, and is located 6 kilometers southwest of Jiayuguan City, Gansu Province. The pass is a trapezoid-shaped military castle. The total length of the castle wall is 733 meters and the height is 11 meters. It is made up of an inner city, wengcheng (barbican entrance to the city), luocheng (outer round defensive wall), outer city and moat. It a multi-tier defensive works. Its western outer wall extends southward to the bank of Taolai River at the foot of Qilian Mountain, and its northern end links with a hidden wall going halfway up the Heishan Mountain. Jiayuguan Pass is entrenched right in the ravine sandwiched in between two high mountains. So it reputed as Impregnable Pass Under Heaven where one defender can ward off the attack by ten thousand foes. Today Jiayuguan Pass is the most intact ancient military building preserved from all the passes on the Great Wall.