The Sanguan Pass on the eastern side of the Helan Mountain some 40 kilometers from Yinchuan overlooks the great desert in the west, and keeps control of a vital road between Ningxia and Alxa in Inner Mongolia. The Ming Dynasty regime built this pass as one of the four major strategic strongholds in Ningxia for defense purposes. Through repeated refurbishments, the Great Wall was extended along the ridge of a precipitous mountain to link with the watch tower and battlement on either end, thereby turning Sanguan Pass into such an impregnable fortress that, as the saying goes, one man alone can keep ten thousand soldiers at bay.