Namhansanseong Namhansanseong ( literally " South Han Mountain Fortress " ) is a park at an elevation of 480m above sea level , immediately to the southeast of Seoul . It is located on Namhansan ( " South Han Mountain " ) . It contains fortifications that date back to the 17th century , and a number of temples . Early history . Tradition connects the site of Namhansanseong with Onjo , founder of Baekje . In 672 , 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 , the during the Second Manchu invasion of Korea 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 in 1627 . He fled with his court and 13 , 800 soldiers to Namhansanseong . 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 to Namhansanseong to mark this event . After the Manchus withdrew , Namhanseong 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 – 76 ) . The grey brick parapets date from 1778 , during the reign of King Jeongjo . Namhansanseong Provincial Park . 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 , Seojangdae ( 西將台 ) , and a single temple , Changgyeongsa , 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 story 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 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 Student Revolution , the monument was destroyed .