Achasanseong — Wikipedia

Achasanseong (Korean: 아차산성; Hanja: 阿且山城) is a Three Kingdoms-era earthen Korean fortress on the mountain Achasan, in Seoul, South Korea. Originally built by Baekje, it was occupied in turn by each of the Three Kingdoms. It is at an altitude of 200 meters above sea level. It has a perimeter of roughly 1 kilometer and an area of about 3375 m2. The first mention of this fortress in historical records comes from the Samguk sagi's statement that King Chaekgye of Baekje ordered it to be fortified against an expected Goguryeo invasion. At that time, Achasanseong would have played a key role in...