Yongin Seokseong Mountain Fortress has been officially designated as a Gyeonggi Province monument.
According to the city of Yongin on Tuesday, Seokseong Mountain Fortress spans an area including the summit of Seokseongsan Mountain across Pogok-eup and Yubang-dong in Cheoin-gu and Jungdong in Giheung-gu. The fortress was built around the 7th century, when the Silla kingdom unified the Three Kingdoms, and remained in use through the Joseon Dynasty. Its walls stretch a total length of 2 kilometers.
In the 6th century, as Silla expanded its influence into the Han River basin, it first built and operated Halmi Mountain Fortress. Around the 7th century, near the time of unification, Seokseong Mountain Fortress was newly constructed behind Halmi Mountain Fortress.
The fortress was initially built along the western ridge where a military base currently stands. It was then significantly expanded through the Goryeo and Joseon dynasties — eastward to include Tonghwasa Temple and northward to encompass the present-day summit of Seokseongsan Mountain. This makes it possible to trace changes in architectural techniques across different periods.
During the Imjin War (Japanese Invasions of 1592), Seoae Ryu Seong-ryong, a prominent Joseon-era statesman, reported to King Seonjo that troops should be stationed at Seokseong Mountain Fortress — given its rugged terrain and strategic location at a transportation hub — to establish a defense line for Hanseong (present-day Seoul) together with Doksan Fortress in Osan and Namhansanseong Fortress in Gwangju.
Despite its deep historical significance, the fortress's value was not widely recognized because a military base had long occupied its core area.
Access was restricted, and some walls were damaged or obscured by military facilities, preventing proper surveys from being conducted.
In response, the city of Yongin carried out a detailed surface survey in 2024 with the military's cooperation. Based on that data, it achieved the designation of the site as a Gyeonggi Province monument.
"We have a great opportunity to make Seokseong Mountain Fortress — hidden for more than half a century — known to the public," Mayor Lee Sang-il said. "Going forward, we plan to actively communicate with the Ministry of National Defense to develop preservation and utilization measures for the fortress."