The Sieges of the Sui-Tang Invasions of Korea, pt. 3
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.
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 1st 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 16th. It fell only eleven days later. On June 7th 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 16th 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 27th 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 18th 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 20th-21st).
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 10th, 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.