Namhansanseong and Bukhansanseong are the south and north parts of the wall and a point of military strategic importance that protected Seoul. The wide basin within the walls could not be seen from outside and made it a perfect fortress. Namhansanseong has the best facilities among Korean castle walls. Especially in December of 1636, King Injo fled to this place and was besieged by the Chong army of 130,000. In the end, he surrendered and signed the Ganghwa Treaty.