Wubei Zhi (Vol. 49)

Treatise on Armament Technology, Volume 135: Principles of Defense

If overlooking a position, rely on steep and secluded ravines where enemy troops find it difficult to mass together; in such cases, one can rely on the terrain to set ambushes.

When choosing a site, if the area is only partially utilized or crowded just as one faces the enemy, avoid it. If the elevation changes too frequently, or if the walls and paths are obstructed, avoid it. If the "veins of the earth" This refers to the geological and environmental quality of the land, often associated with its ability to sustain life and provide resources. are parched and dry, making the drawing of water difficult, avoid it. One must stay far from such hazards.

In recent times, mountain strongholds are easy to defend, while civilian forts are often captured. This is because mountain strongholds have natural features to rely upon. During the Zhengde eraThe reign of the Ming Emperor Zhu Houzhao, 1506–1521., the fall of the Chenjiajian Fort in Yu County The same region where the author served as Vice Magistrate. occurred because the fort was built half on a high mound and half on the plain. Looking up from the front, the strength and weaknesses of the interior could not be hidden; shooting down from the heights, the very roof tiles were shaken. This was a failure to avoid improper terrain.

Second: Avoid Marshes.
"Marshes" refers to low-lying, damp, and saline-alkali landoriginal: "chilu" (斥鹵). Land with high salt and mineral content, typically found in dry lakebeds or coastal areas, which is unstable for construction and corrosive to mud-brick walls.. Because the soil structure is loose, the foundations cannot be made firm. As the ground freezes in winter and thaws in summer, sudden collapses will be frequent. This causes constant labor without any benefit; the fort will not hold even against a brief attack. By the laws of war, such a place cannot be defended.

Third: Avoid Thoroughfares.
"Thoroughfares" are the essential routes that the enemy invadersoriginal: "lu" (虜). Referring to the mobile Mongol forces of the northern frontier. must pass through. Like the paths of great rivers or massive floods...