The theory that has been widely used for the royal city(王都) of Goguryeo is a combination theory of ‘flatland fortress and mountain fortress’ proposed by Japanese scholar Sekino Tadashi(關野貞) more than 100 years ago. This theory is that while inhabitants lived in a flatland fortress, they entered a mountain fortress and defended themselves when wars occurred. However, a detailed investigation of actual literature shows that this theory is not exactly correct.
In Goguryeo, there were both the mountain fortress and the flatland fortress, but their functions were not the same as those in Sekino’s theory. Literature shows that Hwando seong(Hwando Fortress), which is a mountain fortress, was built earlier and was used as a royal castle(王城). Hwando Seong itself was a royal castle, not merely a fortress for refuge. In 244, this Hwando Seong was collapsed and destroyed by General Guanqiu Jian of Wei(魏). Therefore, in 247, a new fortress was built on a plain, which is Guknae Seong(Guknae Fortress). In the early days, the newly built flatland fortress was called ‘Pyeongyang Seong(Pyongyang Fortress)’, but it is considered to be called Guknae Seong(Guknae Fortress) since the reign of King Gogukwon. As Guknae Seong newly served as a royal castle, Hwando Seong was mainly used as a space for rituals. Large-scale ancient tombs were built in front of the entrance of Hwando Seong, and their landscape supported that Hwando Seong was used a space of rituals.
The central village of the royal city was formed around Guknae Seong. It is highly likely that the city was expanded first in the northern region, which was connected to Hwando Seong. In fact, the largest number of gates in Guknae Seong was found around the north wall. Then, the eastward expansion of the city was achieved.
Goguryeo was separated by four rivers: Dongcheon (East River, 東川), Jungcheon (Central River, 中川), Seocheon (West River, 西川), and Micheon (Beautiful River, 美川). Each river served as a boundary and divided into four subregions: Dongyang, Jungyang, Seoyang and Hoyang. Of them, central villages were Dongyang and Jungyang region. Outside of the central villages, huge royal tombs were built. The spatial range of the royal city known to Goguryeo people was probably bounded by Dongcheon in the east and by the range of mountains blocking the west of Hoyang, in the west.