Why does the Great Wall run along the crests of the Yan Mountains?

The Great Wall of China follows the crests of the Yan Mountains primarily to utilize the natural, rugged terrain as a defensive barrier. By constructing the wall along these high ridges, which reach average elevations of 4,900 feet (1,500 meters), builders created a formidable obstacle that was difficult for invading forces to traverse.12

This strategic use of geography is a recurring theme in the wall's history; throughout its construction, builders frequently incorporated natural features—such as cliffs, gorges, and river dikes—to replace or augment man-made fortifications. In the specific context of the northern frontier of Hebei, the Yan Mountains serve as a natural rim separating the North China Plain from the more rugged and inhospitable Mongolian Plateau, making the mountain crests the most effective location for a defensive line.12