Namhan Sanseong (Hanja/English: 南漢山城/South Han Mountain Fortress) is a major park and UNESCO World Heritage Site located at an elevation of 480m above sea level, immediately to the southeast of Hanseong (Seoul), the capital city of Joseon Dynasty. It stands on the Namhansan (Mount Namhan), containing fortifications that date back to the 17th century, and a number of temples.
The fortress is located at 784-16 Namhan Sanseong Avenue/Namhansanseongno, Sanseong-ri 563-beonji, Jungbu-myeon, Gwangju City of Gyeonggi Province, even though the fortress is located on the vicinity of three cities in Gyeonggi Province: Hanam (HagAm-dong), Seongnam Sujeong-gu (Eunhaeng 2-dong) and Gwangju-Gyeonggi (Sanseong-ri, Jungbu-myeon). It can be accessed easily from Seoul through Station 822: Namhan Sanseong Station [남한산성입구(성남법원·검찰청)/南漢山城入口(城南法院·檢察廳)/Namhan Sanseongipgu-yeok (Seongnam Beobwon-Geomchalcheong)/Entrance to Namhan Sanseong (Seongnam Magistrate Court-Prosecutors' Office)] of SMRT Line 8 in Seongnam Sujeong-gu.
Tradition connects the site of Namhan Sanseong with King Onjo, founder of Baekje. In 672 (12th reigning year of King Munmu the Great of Silla), a fortress called Jujangseong (Hanja: 晝長城) was built on the western edge of Namhansan to protect Silla from Tang China. Later the fortress was renamed Iljangseong (Hanja: 日長城). Goryeo kings kept the fortress in repair as a defensive outpost for Gwangju, the nearby provincial capital.
Most of the fortress that exists today dates from the Joseon period. The construction of Seojangdae was planned, beginning in 1624, when the Manchus were threatening Ming Dynasty in China. In 1636 - during the Second Manchu invasion of Korea (Byeongja Second Chinese-Qing Invasion), King Injo of Joseon took refuge in the fortress in an ill-fated attempt to defy the rule of the Manchu Qing Empire Hong Taiji, following the First Manchu invasion of Korea (Jeongmyo First Chinese-Qing Invasion) in 1627. He fled with his court and 13,800 soldiers to Namhan Sanseong. Here they were well defended by the protection of a bodyguard of 3,000 fighting monks. The Manchus were not able to take the fortress by storm, but after 45 days of siege food supply inside ran out, and the king was forced to surrender, giving his sons as hostages and shifting allegiance from the Ming. The Samjeondo Monument (Hanja: 三田渡碑) was erected on the southern route from Seoul (Seoul Songpa-gu) to Namhan Sanseong to mark this event.
After the Manchus withdrew, Namhan Sanseong remained untouched until the reign of King Sukjong, who enlarged it and added Pongamseong on the northeast corner of the fortress area in 1686. Another annex, Hanbongseong, was built along the ridge east of the fortress in 1693. More work was done in the reign of King Yeongjo (1724–1776). The grey brick parapets date from 1778, during the reign of King Jeongjo the Great.
The fortress went unused and slowly crumbled until 1954, when it was designated a national park and a good deal of repair work was done. The fortress area once accommodated nine temples, as well as various command posts and watch towers. Today a single command post, Sueojangdae (守禦將臺), and a single temple, Janggyeongsa (長慶寺), remain. There are other more recent temples on the path up to the south gate and fortress walls. The north, south and east gates have been restored.
Seojangdae is where Injo stayed during the Manchu siege of 1636. The building's second storey was added in 1751, at which time the pavilion received another name, Mumangnu (無忘樓), meaning "Unforgotten Tower". This name apparently refers to the unforgettable shame of the surrender to the Manchus. The shrine of Chonggyedang dates from the same period, and was constructed in honour of Yi Hoe, who was wrongfully executed for his responsibilities in constructing of the southern part of Namhansanseong.
A number of less important historical, sites such as Sungnyeoljeon (崇烈殿, erected in 1638) and Chimgwajeong are associated with the ancient Baekje ruler, King Onjo. Not far from the western wall was the site of Songsu-tap (頌壽塔), a tower with a metal phoenix on top, erected to commemorate President Syngman Rhee's 80th birthday in 1955. When the Rhee government was overthrown in the 1960 April Revolution, the monument was destroyed.