The view that Namhansanseong was the capital of Baekje has been raised consistently ever since the early day of the Joseon dynasty.
Baekje, having established its capital in the Hangang River basin, relocated it several times - to Habuk Wiryeseong, Hanam Wiryeseong, Hansan, and Hanseong - due to both internal and external circumstances.
It seems that people believed that Namhansanseong was one of Baekje’s capitals because of its strategic position and Baekje’s history of moving its capital often.
Most of the historic geographical materials of the Joseon Dynasty, including the Annals of the Joseon Dynasty, Newly Augmented Geographical Conspectus of the Eastern Kingdom, Unofficial History of Korea, Narratives of Yeollyeosil, Cultural Geography of Korea, and Geography of Korea, reveal that Namhansanseong was an old fortress of the Baekje dynasty.
However, Hong Gyeong-mo, the author of A Gazetteer of South Hanseong, quoted the contents of the Writings of Yu Hyeong-won as follows: “Although there is no record of a fortress ever being built on Hansan Mountain, people do not look at the facts but simply state that the ancient capital of Baekje was located on Namhansan Mountain and that Namhansanseong was built by King Onjo. However, the records about the history of Baekje are brief and there are no documentary grounds, so how one can know for sure that Namhansanseong was an old fortress of King Onjo. Therefore, I am writing this at the beginning to express my doubts about this view and to clarify that the fortress was situated below the mountain, not on the mountain.”
Hong Gyeong-mo himself claimed that the capital of Baekje was located in the old town of Gwangju below today’s Geomdansan Mountain, and that “the old fortress of King Onjo” was actually Iseongsanseong Fortress.

The theory of a direct connection between Namhansanseong and King Onjo of Baekje emerged during the Joseon Dynasty.
In 1639, immediately after the Qing invasion of Korea (1636-1637), the Shrine to King Onjo, the founder of the Baekje kingdom, was rebuilt at Namhansanseong, having originally been located in Jiksan-hyeon, Chungcheongdo region during the Joseon dynasty.
With the Qing invasion of Korea, King Injo took shelter at Namhansanseong and sent Kim Sang-seon (Minister of Rites) to the Shrine to King Onjo to hold an ancestral rite there.
In the Joseon society of that time, people understood Namhansanseong to be the ancient capital founded by King Onjo. Therefore, King Injo, who took refuge at Namhansanseong, may have prayed for the spirit of King Onjo in the hope of overcoming the national crisis.
Indeed, such a wish was even manifested in Injo’s dreams.
In other words, as King Injo defeated, in his dreams, the Qing army that attacked Namhansanseong with the help of King Onjo, he relocated the Shrine to King Onjo from Jiksan to Namhansanseong in 1639 right after the Qing invasion of Korea. As the official name of “Sungryeol” was granted to the shrine by the government during the reign of King Jeongjo in 1795, the shrine is called “Sungryeoljeon.”