[Lee Sang-hoon's Korean History] From the Uihwado Retreat to the Fall of Gaegyeong... It Was a Well-Designed Script for the Founding of Joseon

May 22, 1388, Wihwado Retreat of the Liaodong Expeditionary Force; Battle with Choi Yeong in Gaegyeong from June 3
Despite Vanguard Ryu Mansu's Defeat, Yi Seong-gye Remains Calm; Gaegyeong Defense Forces Focus on Blocking Jo Minsu's Left Army
Yi Seong-gye's Neglect Allows Easy Passage Through Sunginmun; Left Army Halts Retreat and Launches Pincer Attack, Annihilating Choi Yeong's Troops

Sanghoon Lee, Professor at the Korea Military Academy

In 1388, Yi Seong-gye departed from Wihwado. Beginning his retreat on May 22, Yi Seong-gye arrived at Gaegyeong on June 1 and engaged in a full-scale battle with Choe Yeong on the 3rd. The Liaodong expeditionary army retreated and camped on the outskirts of Gaegyeong. The right army led by Yi Seong-gye was stationed outside Sunginmun (崇仁門) to the east of Gaegyeong, while the left army led by Jo Minsu was stationed outside Seonui Gate (宣義門) to the west. Although the Liaodong expeditionary army had more troops and supplies than the Gaegyeong defenders, capturing Gaegyeong was not easy.

Gaegyeong was structured in three layers: Naseong (羅城), Gungseong (宮城), and Hwangseong (皇城). Naseong was built utilizing the ridges of Songaksan (489m) to the north, Ogongsan (204m) to the west, Yongsusan (177m) to the south, and Deokambong (108m) and Buhungsan (156m) to the east. The east-west length was 5.2 km, the north-south length was 6 km, and the total circumference reached 23 km. The walls were 8.1 meters high and 3.6 meters thick. It was also called Geumgangseong (金剛城), meaning as hard as diamond. In 1218, the remnants of the Liao dynasty, led by Prince Geumsan (金山王子), invaded Seohaedo and Chungcheong Province, but Gaegyeong was not captured.

On June 3, the Liaodong expeditionary army launched a full-scale attack on Gaegyeong. The right army attacked Sunginmun, and the left army attacked Seonui Gate. However, both were defeated by Choe Yeong’s counterattack. At this time, Yi Seong-gye sent Ryu Mansu as the vanguard to attack. But it is said that he anticipated Ryu’s defeat. The "Goryeosa" records the following:

"When Ryu Mansu was about to depart, Yi Seong-gye told those nearby, 'Mansu has big eyes but no brightness; he is a timid person. He will surely be defeated this time.' And indeed, that happened. At that time, Yi Seong-gye was dismounting and loosening his horse’s saddle when Ryu Mansu fled back. His subordinates reported this, but Yi Seong-gye paid no attention and remained lying inside the tent. Only after repeated reports did he slowly get up, eat, and then order the saddle to be prepared and the horse readied."

This could be interpreted as Yi Seong-gye having the ability to judge generals by physiognomy. However, there is something suspicious about the fact that, as the right army commander, he sent Ryu Mansu to the vanguard knowing full well he would be defeated. Usually, the vanguard is entrusted to the most trusted and capable general because it is useful for gaining the initiative early in battle.

If the vanguard is defeated and returns, it is expected that the morale of the main force will decline. Despite this, sending a general with a losing physiognomy to the vanguard is hard to understand.

What is even stranger is Yi Seong-gye’s reaction when Ryu Mansu returned defeated. Yi Seong-gye showed no reaction while his horse’s saddle was loosened. He displayed composure, ignoring reports of the generals’ defeat in the urgent battlefield. Moreover, preparations for departure were made only after he ate.

Looking further into the "Goryeosa," it states, "Yi Seong-gye entered Sunginmun and coordinated with the left army to advance, and none of the soldiers defending the fortress resisted." Although the historical record states there was no resistance, this is likely a description in the style of the "Yongbieocheonga (Dragon Flying to Heaven Song)." There were defending troops who fought Ryu Mansu earlier, so it is unlikely there was no resistance at all.

Then how should we understand Ryu Mansu’s defeat and Yi Seong-gye’s entry? Although the vanguard Ryu Mansu was defeated, Yi Seong-gye’s main force was waiting outside Sunginmun. It is certain that the Sunginmun defenders were closely monitoring Yi Seong-gye’s main force. However, around the time Ryu Mansu fled back, Yi Seong-gye acted as if he was not preparing to depart by loosening the horse’s saddle. This likely caused the Sunginmun defenders to relax somewhat, and fewer troops were defending than during Ryu Mansu’s attack.

The fact that Yi Seong-gye "entered Sunginmun and coordinated with the left army" suggests that Jo Minsu’s left army had already entered Naseong through Seonui Gate. The left and right armies of the Liaodong expeditionary army attacked Naseong simultaneously. The left army to the west attacked Seonui Gate with full force and succeeded in entering Naseong. Meanwhile, the right army to the east saw its vanguard defeated and fled.

The defenders, struggling with a shortage of troops, must have confirmed that Yi Seong-gye’s right army was not even preparing to attack. They likely shifted a significant portion of the eastern defending troops to the western defense, which had already been breached. In this gap, Yi Seong-gye was able to pass through the weakened defense at Sunginmun smoothly and enter Naseong.

There is a related folktale about a conversation between Yi Seong-gye and an old man working in the fields: "The east gate was open, but you didn’t enter through the east gate and instead tried hard to enter through another gate. Isn’t that foolish? Now, when you entered through the east gate, the east gate wasn’t closed anywhere. So you entered through the east gate and mocked the country. You demanded the country be handed over." This folktale suggests that the attack was concentrated on Seonui Gate to the west of Naseong, leaving the defense at Sunginmun to the east weak.

Choe Yeong’s Gaegyeong defenders initially succeeded in defending Naseong. Afterwards, they attacked Jo Minsu’s left army at Yeonguiseogyo (永義署橋). The exact location of Yeonguiseogyo is unknown, but considering Jo Minsu entered Naseong through Seonui Gate to the west, it is likely a bridge between Seonui Gate and Namsan (南山). After repelling the left and right armies of the Liaodong expeditionary army, the Gaegyeong defenders launched an attack on the left army again at Yeonguiseogyo. They seemed to have considerable military strength.

At that time, the Gaegyeong defenders conscripted soldiers from various provinces to assist. They also blocked alley entrances with gathered carts to establish a defensive posture. Furthermore, they stripped Jo Minsu and others of their official ranks and posted notices on the streets. They declared that anyone capturing several generals would be rewarded with high positions and honors regardless of rank.

However, there was insufficient time to face the large-scale Liaodong expeditionary army. Still, they tried to stabilize military morale by organizing the command structure.

The Gaegyeong defenders attacked and pursued Jo Minsu’s left army, which had entered beyond Seonui Gate. Meanwhile, Yi Seong-gye’s right army, having entered Sunginmun, passed Seonjukgyo and captured Namsan. Namsan was defended by Anso under Choe Yeong, but due to the main force’s desertion, it was insufficient to stop Yi Seong-gye’s right army.

Jo Minsu’s left army being chased by Choe Yeong’s forces may have been due to Choe Yeong’s strong combat power. However, it cannot be ruled out that it was also a deliberate move by Yi Seong-gye to capture Namsan.

Namsan, captured by Yi Seong-gye, was only 103 meters above sea level. However, it was located at the center of Gaegyeong and was the most important strategic point from which the entire Gaegyeong basin could be controlled. During the Korean War in 1950, the UN forces’ recapture of Kaesong (Gaegyeong) also involved controlling the entire city by capturing Namsan.

During the Gaegyeong battle, Jo Minsu’s left army advanced toward Yeonguiseogyo with a black great flag leading but was chased by Choe Yeong’s forces. At this time, Yi Seong-gye’s right army ascended Namsan with a yellow dragon great flag leading. After capturing Namsan, the right army sounded a loud drum. This indicates that the left and right armies of the Liaodong expeditionary army had a prearranged signaling system.

When Yi Seong-gye’s yellow dragon flag fluttered on Namsan and the drum sounded, Jo Minsu stopped retreating and switched to offense. Yi Seong-gye’s right army descended from Namsan and attacked Choe Yeong’s forces from the rear in a pincer movement. The Gaegyeong defenders led by Choe Yeong were annihilated. Choe Yeong had no choice but to retreat to Hwawon (花園).

Eventually, Choe Yeong was arrested, exiled to several places, and finally beheaded in Gaegyeong. The unparalleled hero of late Goryeo, who walked a different path from Yi Seong-gye, thus disappeared.

The Wihwado retreat was based on Yi Seong-gye’s prior preparation and bold decision. The final stage of the retreat was a confrontation with Choe Yeong’s Gaegyeong defenders. Yi Seong-gye defeated Choe Yeong’s formidable army through successful deception and containment operations.

Until then, Yi Seong-gye had never known defeat in battles against the Mongols, Jurchens, Red Turbans, and Japanese pirates. He won again in the Gaegyeong battle after the retreat. Ultimately, Yi Seong-gye took the first step toward founding Joseon by capturing the Goryeo capital Gaegyeong.

Lee Sang-hoon, Professor, Department of Military History, Korea Military Academy

This content was produced with the assistance of AI translation services.