China ancient military defense project. Miracle in the history of world architecture. It starts from Yalu River in the east and reaches Jiayuguan in the west, passing through nine provinces, municipalities and autonomous regions, namely Liaoning, Hebei, Tianjin, Beijing, Inner Mongolia, Shanxi, Shaanxi, Ningxia and Gansu. It is built according to different landforms, mountains and landforms, mostly in the highest part of the mountain, with a total length of more than 7,300 kilometers (14,600 Li), so it is called the Great Wall of Wan Li. Among them, the Yalu River to Shanhaiguan section was seriously damaged due to the simple project. From Shanhaiguan to Jiayuguan, the project is relatively solid and well preserved. The two Guancheng at both ends face each other from east to west, with a total length of 6700 kilometers (13400 Li).