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.

Introduction

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.

History China, Far East, Korea

Sorry for the long delay in updates here on ASW. Anyway this week we will cover the first of the Tang invasions of Goguryeo, launched in 645 AD.

Background

Events had changed dramatically since 613. The Sui dynasty, ravaged by rebellion, had begun to shatter in 615 and by the following year it became clear the Sui could not regain control (at least with their current leadership). In late 617 a measure of peace returned when Emperor Yang’s first cousin, Li Yuan, suddenly seized control of the capital and moved the Emperor into retirement. He took the title Prince of Tang and sought to quell the chaos as regent for a puppet child-ruler. But the former Emperor was assassinated soon after. Li Yuan then took the imperial throne for himself, becoming Gaozu of Tang in 618. Meanwhile in Goguryeo, King Yeongyang died and was succeeded by his younger half brother as King Yeongnyu.

The two empires would spend the following years in cordial relations with each other. As the Tang sought to unify China under their rule they tried to reconcile with the Korean kingdom on an equal basis, exchanging niceties and such forth.

In 626 an internal coup within the Tang imperial family resulted in the abdication of Gaozu in favor of his most able son, the Prince of Qin, Li Shimin. As Emperor Taizong he embarked on a whirlwind campaign of military conquest. By 640 Tang power had become so great that even the Turkic nomadic states had been humbled and Taizong was recognized as Great Khan.

For Goguryeo the years saw the ascendancy of a new leader. Tang excursions had resulted in the construction of a new defense line in Manchuria, the Cheolli Jangseong (Thousand-Li Wall). It was overseen by a rising young military star, Yeon Gaesomun, who came from a prestigious background. Because of internal friction in Goguryeo between the civil and military officials Yeon launched a coup in 642 and killed the King. He placed a puppet ruler in power, King Bojang, and assumed dictatorial powers as Grand Premier.

This played into Chinese ambitions. Emperor Taizong wanted to succeed where Yang had failed, including against Goguryeo. The assassination of Yeongnyu gave him the perfect pretense for war. In April, 645 the Tang army invaded Goguryeo by land and sea.

The Men and the Machines

Both the Chinese and the Koreans had learned important lessons from the Sui invasions. The Tang were well aware that Emperor Yang’s primary problem had always been the issue of keeping his massive armies supplied. Taizong launched a much smaller force of 113,000 men in total, a much easier number to manage logistically. The Chinese also had a far larger naval force then before, including river ships that could navigate the great rivers of Manchuria. This not only gave them more flexibility tactically, it also gave the Tang a steady source of supply for the first phase of operations (before moving too far inland).

Perhaps the most important difference between the Tang and the Sui in approach was that Yang meant only to ‘chastise’ Goguryeo. Taizong intended to annex it outright. On May 1^st the Tang vanguard crossed the Liao River trailed by the naval force and Taizong’s personal cavalry squadrons.

Before moving on we will say a few words about another two Chinese siege machines. The ‘crouching tiger’ traction catapult or hudun pao in pinyin was a medium catapult that roughly fell between the xuanfeng and sijiao in size and firepower. The weapon gained its name from the resemblance of its frame to that a tiger in crouch. Like the sijiao it was one-directional, but like the xuanfeng it was also mobile and could be fired on the move. One purpose of the hudun was to throw incendiary projectiles, which could disperse the enemy in a pinch. However the hudun was adaptable. Common variations include: stationary, cart-mounted, 3 rod arm, and 7 rod arm.

The other weapon we will cover is the chao che. Meaning ‘nest cart’ in English the chao che was one of the oddest Chinese siege machines. Put simply, the chao che was an eight-wheeled cart on which was fixed a tall pole, or a pair of tall poles. By use of a pulley wheel a small house-like box could be lifted and lowered up and down the pole (or poles). What this device was used for is unknown, but most probably it was used as a mobile look-out tower, an artillery spotting platform, or a command platform.

On the Goguryeo side things had changed as well. Yeon Gaesomun had been preparing for a Tang invasion since 643, once it became clear that Taizong was planning an invasion. Yeon placed much of his faith in the hardiness of his soldiers and garrisons and in the impregnability of the Cheolli Jangseong. However the ‘thousand-li wall’ was still unfinished in 645. Yeon had realized this earlier, and so had focused on completing what he judged to be the most important sections of the wall, large fortress-cities that formed the cornerstones of the network.

For our purposes in this article we will focus on these fortress-cities, Ansisong in particular. Much like the Liao River Valley line used by Eulji Mundeok and his successors during the wars with the Sui, the fortress cities of the Cheolli Jangseong were anchored on natural features. Mountains were most common of all, given the most of the wall crossed. However for Ansisong and other fortresses like it the walls played a greater role. The walls of the Cheolli Jangseong were much larger then the walls of the old system and made from stone and packed earth reinforced with clay. Extra defensive measures similar to the ones used by the river fortresses were also used, such as ditches and secondary walls. Permanent stone bastions and forts built into the wall were all well known. The city itself was protected by smaller stone walls dividing it into sections.

The Sieges of the First Tang War: The Battle of Two Minds

The Korean forces found themselves caught off guard almost as soon as the invasion began. The Tang vanguard had crossed the Liao River further north then predicted and put the fortress of Gaemosong under siege on May 16^th. It fell only eleven days later. On June 7^th Ryotongsong, the fortress that had defied the Sui twice, was put under siege. Emperor Taizong arrived a few days later. To the shock of Goguryeo the great citadel fell on June 16^th when the Chinese carried out a massive fire attack on the interior of the fortress. The advance kept up at a quick pace, leaving Yeon Gaesomun having to play a game of catch up. On June 27^th the fortress of Baegamsong fell without a fight, making the remaining fortresses in the Liao River Valley inconsequential. Earlier the Chinese naval forces had landed a sizable marine contingent at the mouth of the Yalu River and captured Bisasong, the southern most fortress-city of the Cheolli Jangseong. On July 18^th the main body of Tang troops arrived before the fortress-city of Ansisong, which was to become the most memorable siege of the war.

However siege preparations were interrupted by an attempt to relieve the city. The Grand Premier had posted two governors, Go Yeonsu and Go Hyezin, in that region and ordered them to prevent the Tang from capturing Ansisong, as the fall of that city would leave the interior open to invasion. However neither of the two generals were skilled at war and at Mt. Zhubi (as the Chinese dubbed it) the Koreans and their nomadic allies (the Mohe, ancestors of the Manchus) were routed by Taizong in a two-day battle (July 20^th-21^st).

The siege itself now began in earnest. Much to Taizong’s dismay, and the cheer of Goguryeo, the walls and garrison of Ansisong held out against the first assault. A stalemate resulted with in a month and the Emperor became impatient. He desired a quick campaign, and the longer Tang forces were held up at Ansisong the less likely it looked that they would be able to clear Manchuria before the rains. The idea was floated to abandon the siege of Ansisong and take another fortress. But Goguryeo resistance had stiffened considerably and Taizong was aware the garrison commander, a Mohe dubbed Yang Manchen by tradition, at Ansisong could cut his supply lines if left unhindered.

The stalemate continued. In early October the Tang, realizing that time was running out, gambled everything on a large earthen mound that had been under construction for the past two months. However on the day of the assault, October 10^th, the mound collapsed and the Tang inexplicitly withdrew. Yang Manchen then took control of the hill, using it to reinforce the walls. In anger Taizong threw much of his army at the breach but on October 13th he ordered a withdrawal of all Tang forces. The first Tang invasion was at an end.

Eventually the Tang would return. Yeon Gaesomun and his regime were significantly strengthened by this victory and Taizong planned a second invasion. Before he could the Tang Emperor passed away in 649, and invasion plans were called off until 660. This war will be covered in the next installment.

History China, Far East, Korea