On my last update, I covered the first of the Tang invasions of Goguryeo. This week we will cover the second Tang invasion, focusing on the siege of Pyongyang.
The failure of the first invasion was the trigger for future conflict. Tang Taizong had never accepted his defeat at Ansisong and laid plans for future conquest. Border skirmishes and deep raids became the norm all along the northeast. Taizong’s death in 649 and the ascension of his son Li Zhi to the throne as Tang Gaozong had brought a respite. In Goguryeo the unyielding Grand Premier, Yeon Gaesomun, planned to take advantage of the lull. In 654 it was broken when a Goguryeo expedition threatened Tang client states on the steppe.
The Tang response, when it came, struck at an unusual direction. Emperor Gaozong knew that to take down Goguryeo would require an attack from more then one direction. To this end he had continued his father’s diplomatic offensive in Korea, cultivating a relationship with the kingdom of Silla, Goguryeo’s most powerful rival on the peninsula. In 660 the King of Silla called for aid against Baekje, Goguryeo’s ally on the peninsula. Gaozong responded by sending an expeditionary force. Together the allied forces conquered Baekje, turning it into a Tang province. In an instant, the entire strategic balance of power in Northeast Asia had changed.
The success of the campaign against Baekje had emboldened the Tang, and they hoped to use their momentum against Goguryeo the following year. The leading commanders on the peninsula lead by Su Dingfang were placed in charge of this campaign. In August 661 these forces were sent across the sea, bypassing the Cheolli Jangseong, and landed. The Emperor accompanied the expedition to oversee the war.
The Men and the Machines
Tang and Goguryeo had both been preparing for this inevitability. During the years between 645 and 660 both the Chinese and the Koreans had gained much experience and fighting the other. These lessons proved invaluable. Territorial advances along the Liao River line had pushed the border further into Manchuria. An attack directly on Pyongyang thus became possible, even though the fortress-cities remained a concern. Chinese naval forces continued to exercise almost total control of the waves. Logistical concerns had already been taken care of earlier as the supplies gathered for 649 were now used to supply the expedition. In addition, Silla promised military and logistics support to the Chinese.
As before, the aim of the war was to annex Goguryeo. By capturing Pyongyang the Tang hoped to force the surrender of the Grand Premier, thus ending the war. Coordination with Silla, and their chief general Gim Yusin in particular, played a role in this. While the Chinese handled affairs in the north, it was the job of Silla to keep them tied down in the south and give support to the forces in former Baekje territory. Armed resistance was continuing at this time, and the support of Silla was crucial to keeping the territory under control.
Before moving on we will cover our last Chinese siege weapon. Perhaps one of the most famous siege machines in East Asia was the siege crossbow, or chuangzi nu in pinyin (meaning ‘little bed crossbow’). These weapons were oversized crossbows mounted on a table frame originally. This is how it gained its name. By Tang times they had become far more sophisticated and powerful. Tang chuangzi nu used double bows (facing in opposite directions), increasing the draw power significantly. The uses of the chuangzi nu were varied, and could be used to good effect both for offense and for defense. Mobility was an important feature of these weapons, and functioned in a similar role to later horse artillery in that way. Common variations include single bow, double bow, stationary, mobile, and battery (multiple weapons mounted on the same frame).
On the Goguryeo side of the war preparations had been underway for some time. Yeon Gaesomun was no fool and knew that his army would be unable to deal with a protected war. Now they would be forced to deal with two theaters, north and south. The garrisons had been tired out by the long watch on the border zone and were demoralized. But the Grand Premier had not given up. He focused his great energy on insuring the defense of Pyongyang, taking measures to ensure the integrity of the city walls and the mountain fortresses that surrounded the capital. Yeon did not take command the garrison in person however, and instead intended to remain mobile, commanding the capital armies and his personal militia. He also committed other armies to the field, both to support him and deal with Silla.
The much-vaunted Cheolli Jangseong would not play a role this war. While completed in 647 to great fanfare in Goguryeo the nature of the Tang invasion, an oversea surgical strike, meant that it would not come into play in any major fashion. While Chinese armies did operate in that region, they did not engage the wall.
The Sieges of the Second Tang War: The Last Victory
The initial landing went without trouble. The Tang quickly established base on the coastline and Gaozong set up headquarters. However, misgivings within the court over yet another invasion of Goguryeo, as well as the objections of the Emperor’s strong willed consort, Wu Zhao, forced him to withdraw. Affairs were left in the hands of his chief commanders: Su Dingfang and Qibi Heli (a Tiele or Siberian chieftain serving Tang). Within weeks, Su had crossed the Taedong River, defeating a Goguryeo field army holding the banks, and by late August /early September, he had put Pyongyang under siege. The headquarters of the besiegers was set up at Mt. Mayi, a strategic choice.
Now the siege began. Besieging Pyongyang was no easy matter and was complicated by the mountain fortresses surrounding the city. An attack direct on the city walls was not probable as long as the fortresses remained intact. From these vantage points the garrisons could rain down fire on the Tang besiegers, catching them in cross fire between the walls and the mountains. The mountain holdfasts would have to reduced first before Pyongyang proper could be put under siege. As the Sui engineers of that dynasty’s third invasion would have testified, trying to crack a fortress built onto the sides of a mountain was difficult.
However outside developments appeared to aid the besiegers. Yeon Gaesomun knew the Chinese would attempt to link with their allies in Silla (which he was struggling to contain) and put a garrison on the Yalu River to stop the second column from crossing. The attempt failed spectacularly (around October 661) and one of the Grand Premier’s sons, Yeon Namsaeng, was almost killed. Morale plummeted drastically. However Su Dingfang recalled the victorious troops before they could cross the Yalu to take part in a troop rotation, giving the defenders time to recover. Winter proved to be the Tang’s greatest enemy, as it proved unusually harsh, even for northeastern Korea. But Su did not suspend operations, but was preparing for a big push in the coming spring.
The following year, 662, the Chinese tried to reinforce their positions. As winter ended Emperor Gaozong dispatched additional forces from northeastern China into Manchuria to aid Su Dingfang in his siege of Pyongyang. Yeon Gaesomun heard of this and set a trap for the relief column near the Sasu River. As the Tang troops attempted to build a fort along the banks, the Goguryeo forces descended on them. Pang, his sons, and men were all slain. Using this momentum Yeon swung his army towards Pyongyang and smashed into the siege camps. Su Dingfang attempted to hold on grimly but following a spring blizzard quit the siege, using the weather as a convenient cover in more ways then one.
Goguryeo had managed to defeat the sixth major Chinese attempt against it (four by Sui, two so far by Tang), but the kingdom’s luck was running out. Despite the failure of the besiegers to take Pyongyang or cross the Yalu the conflict proved the deadly effectiveness of the Tang-Silla alliance. The northern-most of the Korean Three Kingdoms now stood alone. Goguryeo was only able to hold out by virtue of the strength of Yeon Gaesomun and the effect he had on his soldiers. When the Grand Premier died in 666 it all fell apart. This will be covered in our next, and final, installment.