Gubeikou, situated in Beijing's Miyun County, is 125 kilometers away from Beijing proper. It has long been a town of military significance and an important passage to the capital city. The Yanshan Range winds from east to west and is cut off at Gubeikou, forming a natural narrow pass here. To the west of the pass are the Chaohe River and the Wohu Mountain, and to the east is the Panlong Mountain.
The main part of today's Gubeikou Wall was constructed under the supervision of Xu Da, a noted general in the Ming Dynasty. It runs for more than 20 kilometers and consists of four sections: Wohushan, Panlongshan, Jinshanling, and Simatai. It has 143 beacon towers, each positioned at an average interval of 156 meters. The nearest two are only 30 meters apart. The inside of these towers varies in design. While some have a flat ceiling, others either have an arched ceiling, a domed ceiling, or an octagonal, painted ceiling. Each tower has two floors, six archways, and ten arched doors, allowing garrisoned soldiers to advance and retreat freely. The towers are also different in size. The largest one can accommodate a garrison of 100 soldiers, and the smallest one a garrison of 10 soldiers. The towers often have one to six portholes.