Namhan Mountain Fortress (南漢山城, Namhansanseong) is surrounded by a more than 8km long that follows rugged terrain some 500m above sea level. The geological location allows a relatively small number of soldiers to resist a much larger force with ease. The main fortress wall (not including the outer walls and semicircular secondary walls built in front of the gates) is 7,545 meters in circumference, and the compound inside the wall covers 2,126,637 square meters. The walls total 12.356km in length when the auxiliary sections are included.
The main wall was built upon the foundation used for the walls of Jujang Fortress, which was erected on the same spot in 672, during the Unified Silla Period. The outer wall was built at various times and shows a mixture of construction methods, ranging from Unified Silla to Joseon. Indeed, Namhan Mountain Fortress is like an encyclopedia of Escarp-building techniques used on the Korean Peninsula for more than a millennium. As such it is a very important historical object for understanding the development of Korean fortress construction over time.