Asan-si plays a part of the gateway to Chungnam as it is located at the central part of the
Korean Peninsula, and the northwesternmost Chungnam; further, Asan-si is also in proximity to
Cheonan, Yesan, Gongju, Pyeongtaek areas.
Baekje Kingdom was the state which built more mountain fortresses than Goguryeo or Silla.
According to the ancient records, Tangjeonseong Fortress was built during the 36th ruling of
King Onjo (A.D. 18).
Afterwards, Tangjeongseong Fortress was highlighted in its natural geographic importance as it
came to border on the areas south & north of Charyeong and Geumgang in the process of
territory expansion in early Baekje Kingdom. Also, with Baekje Kingdom transferring its capital
to Wungjin due to the southward expansion policy of Goguryeo, the whole area of Asan Bay
near Tangjeongseong Fortress became the military base of the front lines against Goguryeo,
which triggered construction of defensive mountain Fortress in great numbers in this area.
Tangjeongseong Fortress during the period of Baekje Kingdom is inferred as Asan-si
Eupnaedong Mountain Fortress and its affiliated mountain fortress- Baebangsanseong Fortress,
and the many mountain fortress built at the northern mountain range of Onyang, and the whole
ares of the Gokgyocheon Stream took charge of the defensive role against Goguryeo and Silla.