The tunnels built during the Three Kingdoms Period were more than ten miles underground in Bozhou and cruciform in the city. Cao Cao's military secrets are rarely recorded in historical books. In the 1970s "deep excavation, extensive grain accumulation" was discovered again. So, the most authentic and reliable. The tunnel is not wide. The coupons on both sides and on the top are brick, which can be used for one person to walk. There are many kinds of military facilities in tunnels, such as cat's ear holes, traps, baffles, and the works of more than a thousand years ago have such functions, which are amazing.