Extended Defensive Wall

The defensive walls of Namhansanseong largely consisted of two parts, the Bonseong or Wonseong (fortress body), which was built during the reign of King Injo (r. 1623-1649) of the Joseon dynasty, and the Oeseong (extended defensive wall), which was built during the reign of King Sukjong (r. 1674-1720), also of the Joseon dynasty. The fortress body generally covers the area protected by the old fortification (called the Jujangseong), which was originally built during the Silla period and renovated during the reign of King Injo, whereas the extended part of the fortress consists of the Bongam Extended Defensive Wall, Hanbong Extended Defensive Wall and Sinnam Outwork. The newer walls were designed to exploit the distinct physical features of the mountain ridges branching out in an east-west direction from the main ridge of Cheongnyangsan Mountain, which runs from south to north.

The construction of the extended defensive wall started in the third month of 1686, when Yun Ji-seon (1627-1704), then the Yusu of Gwangju, proposed the reinforcement of the fortress body by building an Bongamseong (auxiliary fortification), and provided labor drawn from the Sueocheong Army Corps Headquarters, along with financial support of about thousand-seok of grain (one seok is equivalent to approx. 180 liters). The construction work took fifty days to complete, resulting in the creation of a 300-meter-long wall with 294 merlons, 4 auxiliary gates, and 15 guard towers. A record of the construction of Bongamseong was found engraved in regular script on a natural stone used in the fortification
.
The Hanbong Oeseong (second auxiliary fortification) was built in 1693 under the supervision of O Si-bok, then serving as the Sueosa. Unlike the Bongam Extended Defensive Wall, which completely encloses the mountain top, the Hanbong Extended Defensive Wall was designed to provide a direct, safe passage to the summit of Hanbong Peak. The fortification was originally 851 feet in circumference, and had 227 merlons and one auxiliary gate. Part of the fortification was demolished in 1705 at the command of a Qing envoy, but the entire fortification was renovated in 1739 by Jo Hyeon-myeong, then the Sueosa, in order to create a 895-feet-long wall and 272 merlons. This was also the year that his successor Min Jin-hu continued to renovate the fortification, placing two batteries on Bongamseong, along with a casemated embrasure, so that it could join the gun on the Janggyeongsa Outwork in a pincer attack against an enemy assault.
The renovation project led by Min Jin-hu in 1719 created a fortified area with a circumference of 743 feet, complete with 238 merlons and a casemate, which are now called the Sinnam Outwork and Namgyeokdae, respectively. Built on the summit of Geomdansan Mountain (534 meters), about 2.6 kilometers south of the fortress body, the renovated fortification was occupied by Qing forces during the Byeongjahoran, and was used to launch an artillery bombardment against the defending Joseon forces. The extended fortification had two observation towers in 1753, completing the system of defense of the temporary royal palace, which would eventually play a key role in defending the capital of the Joseon Dynasty.