The Attack on Goguryeo by King Muryeong of Baekje and the Northern Border Line

During his 23-year reign, King Muryeong of Baekje (501-523) primarily focused on military activities. According to the Samguk Sagi (History of the Three Kingdoms), King Muryeong's military operations were primarily concentrated in the northern regions, including Goguryeo and Malgal. This marks a clear difference from the military activities of his predecessor, King Dongseong, who engaged with neighboring countries such as Goguryeo, Silla, and Tamna. Upon his ascension to the throne, King Muryeong immediately attacked Goguryeo. This marked the first preemptive attack on Goguryeo since the 15th year of King Gaeru's reign (469). Subsequently, he continued to engage in battles against Goguryeo. Goguryeo's King Munjamyeong responded to Baekje's aggression by either leading Malgal forces or actively countering with Malgal's support. However, after suffering a crushing defeat at the hands of the cavalry led directly by King Muryeong in the Battle of Wicheon, Goguryeo ceased further warfare with Baekje. At that time, Goguryeo was focused on diplomatic relations with the Northern Wei and consolidating its internal affairs. Additionally, tensions with Silla, which was expanding northward, posed a significant challenge. Given these circumstances, Goguryeo was not in a position to engage in full-scale warfare with Baekje. During the early years of King Muryeong's reign, there were attempts to advance northward, even reaching Sugokseong Fortress in Shin'gye, Hwanghae Province. However, most of the conflicts with Goguryeo occurred in Yeoncheon and Pocheon in Gyeonggi Province. Therefore, the northern border between Baekje and Goguryeo during King Myryeong's reign can be considered the line between the Imjin River and the Han River, north of the Han River in the northern region of Gyeonggi Province. During King Muryeong's reign, the Han River basin controlled by Goguryeo was limited to the southern Han River northeast of Baekje. The posthumous title 'Muryeong-wang' reflects the military achievements garnered from the wars with Goguryeo.