Hailongtun Fortress, known as Longyantun during the Song and Yuan dynasties, is located east of Longyan Mountain in Taiping, Zu-nyi County, about 12 miles from the city of Zunyi. The fortress is situated on top of mountains surrounded by steep cliffs and flanked by streams, with only one narrow path at the back of the mountain leading to it, where it is said a single armed man can stop an army. Ancestors of Bozhou Tusi (chieftain) Yang Ying-long took advantage of the topography by building a 3-mile complex of earthen walls and intersecting circu­lar enclosures as well as tall buildings, warehouses, and water prisons. The fortress area consists of nine passes, including Bronze Column, Iron Column, Flying Drag­on, Fly Phoenix, Chaotian, and Wan'an; they are con­nected by walls extending more than 3 miles along the mountain. As China's only extant ancient military fortress, with its grand scale and well-preserved walls and facilities, Hailongtun has become an important resource for studying the Tusi (official title for lo­cal chieftains among some ethnic groups in the old days) system and the many passes in the southwestern region.