Mìyún

Miyun lies northeast of Beijing, where the roads to the northern frontier pass through mountain valleys. Gubeikou, on the Chao River, was one of the important gateways through these ranges. The Ming strengthened its walls and passes, and the general Qi Jiguang later rebuilt sections of the Great Wall and added watchtowers. In 1572 he held a major military exercise in the river valley near the pass.