Watchtower at the Chinese Great Wall

Watchtowers are the key part of the military construction. Very close to each other, brick towers in square are built atop the Wall. A famous general Qi Jiguang in Ming Dynasty had ever mentioned the specifications and structure of the watchtower in his On-the-Spot Record of Military Training. It describes the watchtowers are about 36 meters wide and10 to 12 meters high. They built the tower at a distance of every 10 or 100 footsteps at the crucial parts, and every 52, 140 or 200 footsteps at other parts. Neighboring watchtowers can support and reinforce each other during the war.