Reevaluation of the Northwestern Border of Goryeo in the Liao(遼) and Jin(金) Dynasties: Focusing on Boju(保州)

During the Liao(遼) and Jin(金) dynasties of the Goryeo(高麗) period, Goryeo's northwestern border was defined by the Yalu River(鴨淥江), and Boju(保州) was located at the northwest end of Goryeo's six eastern provinces. During the Japanese colonial period, Tsuda Soh Ki-chi(津田左右吉) redefined the scope of the six eastern provinces to include the coastal areas of present day Pyonganbuk-do within the current Yalu River, a view that our academic community currently follows. However, recently, based on research suggesting that the Yalu River during the Goryeo period was the Liao River, an argument has been made that the six eastern provinces of Goryeo should be viewed as lying between the opening of Kaixian and Cheollyeong in China. Nevertheless, issues remain regarding Goryeo's northwestern border and the Yalu River. Firstly, the misconception arises from examining the direction not as true north(眞北) but as mapped north(圖北), leading to an erroneous consideration of the west as northwest. Secondly, place names can change, and the same applies to the boundary river, the Yalu River. Therefore, the Yalu River should not be seen as a proper noun referring to a specific river but rather as a common noun meaning “boundary.” The fact that the Yalu River has many names suggests that these are not different names for a single river but rather names that indigenous people in the region have given to rivers that have become the new Yalu River due to changes in the border. Considering these points, the author reevaluated the records of Goryeo and the Liao(遼) and Jin(金) dynasties regarding Goryeo's northwestern border and the Yalu River. As a result, it was argued that Goryeo's northwestern border included the areas of Jilin(吉林), Jangchun(長春), and Nang'an County(農安 縣) in Jilin Province, China, and that the Yitong River(伊通河) flowing through this area should be considered the Yalu River as the border. Additionally, it was noted that Boju, located at the northwest end of the six eastern provinces, corresponds well with the Nang'an County area.