The most obvious characteristic of Namhansanseong lies in its topographical advantage; there is a spacious, flat top called Gorobong, with a low center and high sides over 480 m above sea level, as well as being a high mountain over flat lands for easy observation of the surrounding area. Due to these traits, Namhansanseong had served as a command post since the Unified Silla era in the 7th century. Unified Silla constructed the Jujangseong fortress where Namhansanseong sits today to house men and to stock supplies when it was fighting the Tang Dynasty in the 7th century. In the 13th century, during the Goryeo Dynasty, Namhansanseong was a stronghold against the Mongol Invasion. Since the 17th century, Namhansanseong, near the capital city of Seoul, grew greatly in size as a mountain fortress, serving as an emergency capital for the King of Joseon.