The Bukhansanseong (Korean: 북한산성; lit. fortress of the mountains north of the Han) is a fortress located in Gyeonggi Province and Seoul, South Korea, dating back to the middle Joseon period.^[1][2] The present fort was completed in 1711, though plans for the structure date back to 1659. The name is also given to a fortress mentioned in the Samguk Sagi, constructed by Gaeru of Baekje in 132 CE, and the two are often conflated although the putative connection is contested.

The modern Bukhansanseong was built to protect the approach to Seoul, filling a gap in Korea's defences that had become apparent during the second Manchu invasion of 1636 and the earlier Imjin War. The Bukhansanseong was used as a royal retreat in emergencies, and contains 120 rooms.

Total length of Bukhansanseong Fortress is 12.7 km and total area of the Fortress is 6.2 km².^[8] There were 6 great gates, 8 secret gates, 2 water gates, and 143 seong-rang (Korean: 성랑, sentry post)

Bukhansanseong Fortress also has one Temporary Palace, three Jang-dae (Korean: 장대, Commanding Post), three Yu-young (Korean: 유영, Military Camp)for defensive purpose. Three different units were stationed in Bukhansanseong Fortress, called Sam-gun-mun (Hun-ryeong-do-gam, Geum-wei-young, and Eo-young-cheong). They were stationed in three different location within Bukhansanseong Fortress, and the main responsibility of those units was the protection of the Bukhansanseong Fortress.

13 Buddhist temples were also established within the wall of Bukhansanseong Fortress for Buddhist monks soldiers. Only 6 Buddhist temples remain today, but all lost temples are designated as historical site.

In addition, 7 Armories, 99 wells, and 22 small reservoirs were under the control of Bukhansanseong Fortress.^[9]

• Namhansanseong
• History of Korea
• List of fortresses in Korea
• Hwaseong Fortress