明代以前,一片石是一条京秦之间的交通要道。到了明洪武十三年(1380年),著名将领徐达奉旨修筑九门口段长城,竣工后,徐达大将军和设计师们根据九门口所处的险要地理位置,设计开掘出一条从长城内侧校军场,不经九门城关,而秘密直通关外的山中暗道,这条坐落在长城下面山体中的暗道全长1027米。这条暗道共有两个出口和一个入口。其中一个出口为一片石战场,另一个出口通关外。暗道内有29个大 Before the Ming Dynasty, a piece of stone was a traffic art between Beijing and Qin. To Ming Hongwu thirteen years (1380), the famous general Xu Tatsuo built nine gate section of the Great Wall, upon completion, Xu Da generals and designers according to the location of Jiumenkou in the critical location, designed to dig out a from the Great Wall Inside the military academy, without passing through the nine gates, but secretly pass off the mountain illegal channels, this is located in the mountain under the Great Wall in the tunnel length of 1027 meters. This illegal passage has two exits and one entrance. One of the exits is a stone battlefield and the other is outside the customs clearance. Inside the illegal road there are 29 large