The defensive structure shown here is an outwork designed to defend a gate or specific section of the curtain wall of a fortress. As for Namhansanseong, there are five such facilities, each of which had a battery at the end. The defensive work built on Yeonjubong Peak measures 315 meters in circumference and covers an area of 865㎡, and originally had 73 merlons, as well as – according to the Map of Namhansanseong – a battery which no longer exists. The current work was restored after the excavation carried out in 2000 by a team from the Land and Housing Museum.