Eupseong was the town surrounded by wall in Korean history.
Feudal system in Korean history was very short, so the construction like castle could not developed in Korean history.
You might be curious “So what is the Korean castle in AOE2?”
That was the one of many eupseongs, not castle.
That is the wall surrounding Suwon in Kyeongi province in Korea.
Kyeongi province is surrounding Seoul. Seoul is located middle of Kyeongi province.
If you visit Suwon, you can see real one.
the word “Eupseong” is came from Chinese characters.
Many Korean word was came from Chinese characters, because Koreans used Chinese characters very long time.
“Eup”(邑) means town.
“Seong”(城) means the town surrounded by wall. Also it can be translated by castle.
In middle age, Koreans called capital as “Dosoeng”
Do(都) means capital.
In middle age, Korean “Yangban” ,Korean gentry class, loved to use Chinese characters.
They thought Korea was small China, and they were proud of it.
However normal people called capital as “Seoul”
Seoul in middle age in Korea was not place name.
The old name of Seoul was “Hanyang”.
Seoul was just normal noun meaning “capital” in Korean middle age.
Also, Seoul is Korean ordinary word. This is not came from Chinese characters.
So If I say “the Washington DC is seoul of USA” This make sence.
During under control by Japanese Empire before the end of World War II, Japanese government general changed the name of our capital from Hanyang to Kyungseong.
Kyungseong also means capital, but Kyungseong was not acceptable to Korean people.
It was accepted to symbol of Japanese government general to Korean people.
So Hyeongmin Kim ,the mayor of Kyungseong, changed the name of your capital to “Seoul”
And Hyeongmin Kim became the fisrt mayor of Seoul in Korean histoty.
Today, many Korean people don’t regard seoul as normal none meaning capital anymore. they use “sudo” instead.
“sudo” is alse meaning capital, but this is came from Chinese character.
But Seoul is still meaning “capital” in Korean language.