Shanhaiguan is not the first Great Wall pass built, nor the closest to Beijing, because it is to rush, there is the reputation of "two Beijing lock keys without double land, the first gate of the Great Wall". Kangxi Emperor once had a poem praise: the heavy customs are called the first, and the danger is leaning on the edge. The Great Wall is connected to the terrain, and the sky is connected to the sea. Shanhaiguan is not only a pass, but also a city pool, the whole Shanhaiguan city as the gate, is an important part of the Great Wall of China. It is a complete, rigorous and scientific ancient city defense complex and military defense system with the Great Wall as the main line and Guancheng as the center, including 7 acropolis, 10 major passways, dozens of city platforms, enemy platforms, campfire platforms, etc.