Korean fortress

[2] Korean fortresses were based on a stone culture and built with stones on natural mountainous terrain; therefore, they are conceptually completely different compared to Chinese fortresses, which were based on an earth culture and built with bricks and stamped earth on flat land.

[5][8] Korean fortresses were invented by Goguryeo and spread to Baekje and Silla,[9] and then inherited and further developed by Goryeo and then Joseon.

[5] Most Korean fortresses are single layered wall structure surrounding a city, town or a village.

The purpose of the mountain fortress was to enable the inhabitants of the city, town, or village to escape into during emergencies caused by war or insurgencies.

Some of the larger ones contained HaengGung, which are small Royal Palaces designed to accommodate the King who may have fled to that location.

Samnyeonsanseong , a Silla mountain fortress in central Korea, built in AD 470 as a defense against Goguryeo Kingdom.
Namhansanseong was the site of a siege by the Manchu invaders, where the Korean King surrendered to the Manchus after a 41 days siege in 1637.
Hwaseong Fortress of Suwon, built in 1796. This is a city wall.
This is an example of a walled city gate. A smaller wall protects the entry into the city gate. Dongdaemun , Seoul, the East Gate, built in 1398.