Thanks. I know they mention south of Seoul but I can't seem to find the actual location because when I searched for it in a Koren map, it turned out to be east of Seoul.
Anyway James Lewis, in his book The East Asian War, describes Chiksan as a border town in between Gyeonggi and Chungcheong province. So based on those two sources, the correct place may indeed be south of Pyeongtaek (Gyeonggi province). It is in the northern part of Chungcheong province.
The reason for my confusion is the romanisation of the name. Western accounts spell it Chiksan so I searched for 칙산 which led me to the wrong area. It is actually 직산 which should be romanized as Jiksan.
Thanks for pointing this out.
