Last week on this blog I posted the first part in my series about the Sui-Tang sieges during the invasions of Goguryeo. This week, the second part, will cover the siege of Ryotongsong, the main action of the third invasion of Goguryeo launched by the Sui in 613 AD.

Background

The events of the previous invasion had barely fazed the Sui monarch. Unwilling to accept his defeat, Emperor Yang announced a renewed invasion in January, 613. The Chinese took precautions to avoid the problems that had plagued them in 612: extensive measures were taken to make sure the army remained in supply across Manchuria. Emperor Yang also granted his commanders almost total autonomy, so the Korean garrisons would not be able to exploit command delays. However ominous rumblings of rebellion, as well as a horse shortage, cast a pall over the expedition.

On March 30^th the third invasion of Goguryeo was launched. On the Korean side King Yeongyang remained confident the fortress line would be able to hold out, but still took added precautions across the fortress line and in the mountain fortresses near Pyongyang.

The Men and the Engines

Sui invasion forces crossed into the Liao River Valley in Late May. The army then broke off into three columns with the Emperor mandating that Ryotongsong and Sinsong must be captured. The third column was directed to make an overland strike at Pyongyang in conjunction with naval forces coming up from the Shandong Peninsula.

The best known siege of this war is the siege of Ryotongsong. Commanded by the Emperor in person the besiegers were prepared to use the full force of their arsenal against the garrison. For our purposes we will cover another two siege machines leading on from last week.

In addition to the already mentioned xuanfeng catapult and yunti che ladder another weapon employed by the Chinese was the ‘four-footed’ traction catapult. Called sijiao pao in pinyin it gained its name from the four large wooden columns that formed its legs and provided the corners of the frame. The sijiao was largest of the Chinese traction catapults, standing a good four times the height of the average adult man. Its primary purpose was the reduction of walls, a task it did well. Unlike the xuanfeng, the sijiao was one-directional. However it could be made mobile through being mounted on a cart (though it was never fired while mounted). The weapon could be adapted through increasing or decreasing the number of bundled rods that comprised its throwing arm. Common variations were: five rod arm, nine rod arm, ten rod arm, and thirteen rod arm.

The other siege weapon we will cover is the assault cart. Called chong che in pinyin the assault cart was the Chinese version of the well-known siege tower. Like any siege tower the chong che was a wheeled cart on which was built a makeshift tower. There was no typical chong che because each was built to fit the circumstances of the specific siege in which it was involved, as they were built on the field. This allowed much adaptation and flexibility. One famous chong che type was the so-called ‘cloud bridge’, a massive 100-meter tall weapon armored by layers of cowhide on the sides. The top level contained many bags of water to douse fires.

In the time between the sieges of 612 and the sieges of 613 no major changes took place on the Korean side of the war. However we will cover in brief the importance of natural obstacles in Goguryeo defense strategy. As already mentioned last week the most common of the Manchurian fortresses were anchored between a river and its tributary, which provided a natural defense line. Other fortresses were built on the sides of or anchored onto a mountain. Pyongyang was protected by a network of such mountain-fortresses, which made the city nearly impenetrable.

Historical records also point out that sometimes the garrisons of a particular fortress would try to extend the walls to take advantage of a nearby natural defense. Ryotongsong was one such fortress. While already anchored on the Liao River the garrison successfully extended the walls to a nearby mountain (probably between 612 and 613), causing the Chinese endless frustration.

The Sieges of the Third War: Near Victory and Disaster

From the beginning the Chinese assaulted the Manchurian fortress line with far greater force then the previous year. Sui military engineers unrolled a much greater part of their siege arsenal in the third invasion then they had in the second. Ryotongsong was hit the hardest of all. Emperor Yang knew the fortresses’ importance and directed that it be hit from all four directions at once unceasingly.

But the Korean garrison held on grimly. Each move made by the Chinese was countered by the garrison successfully. One celebrated episode was a mass assault on the walls by the Sui using yunti che assault ladders and battering rams. This was driven off by the Goguryeo garrison through use of fire, burning them as the machines got caught in the ditch system in front of Ryotongsong. Another incident involved a different tack. Emperor Yang decided to attempt to take the fortress through tunneling, but the garrison had been expecting such a move. As the Chinese siege engineers dug towards the walls the defenders flooded the tunnels with water from the nearby river, drowning them out.

However the Sui Emperor had another card to play. After the siege had been going on for a month the Emperor tried another ploy. He ordered the construction of a great earthen ramp along one corner of the fortress wall. To protect the engineers and laborers as they worked eight chong che manned by the best archers in the Sui forces were built and rolled out near the walls. This time the Chinese met with success. The defenders were forced to abandon the section of the wall threatened by the ramp under withering arrow fire. On July 20^th as the Sui prepared to storm the walls of Ryotongsong disastrous news arrived from China. Yang Xuangan, the son of the late popular Premier Yang Su, had risen in revolt and threatened the imperial capital of Luoyang itself.

The situation had drastically changed. Emperor Yang suddenly found himself facing the possibility of being caught between a rapidly growing rebellion at home and the forces of Goguryeo at the front. He acted immediately, recalling the advance column and the naval arm and directing them to make all haste to the heartland. The entire war was called off and the Sui withdrew with barely disguised hurry. King Yeongyang of Goguryeo and his generals could barely believe it, especially as false retreats were a well-known Chinese trick. But the hurry in which the Sui evacuated and several defections led them to infer it was real.

Eventually while the Sui would mount one more invasion the following year (614) the third invasion was the last major offensive. Yang Xuangan’s revolt had lit the powder keg of discontent, leading the Sui Empire to unravel and fall in 618. Goguryeo survived but just barely, and would go on to face the successors of Sui: Tang.

The first of these invasions will be covered in the part three of my series.

History China, Far East, Korea