Boju, 506 BCE: Five Battles Won, One Kingdom Lost

The problem

Chu was the largest state in the middle plain. Wu was a small state on its eastern edge, and in 584 BCE Wu had already taken the Chu city of Zhoulai; over the following seventy years the two states fought ten wars and Wu won most of them. The rising power in the north, Jin, had found a use for Wu: it sent the exiled Chu minister Qu Wu with a train of war-chariots to teach the Wu army to fight with chariots, so that a small army on the eastern flank could tie down Chu’s attention while Jin dealt with Chu from the west.

The campaign of 506 BCE also carried a personal motive. Wu Zixu (伍子胥), a Chu official whose father and brother had been killed on the order of King Ping of Chu, escaped to Wu and spent years waiting for the moment when Wu might strike. King Helü (闔閭), who had taken the throne of Wu in 515 BCE, gave him the position the moment it was useful.

The six years before the battle matter as much as the battle. In 512 BCE Wu destroyed the small states of Xu and Zhongwu, which Chu had taken as vassals, and then — on Wu Zixu’s advice — split its army into three columns and spent six years raiding Chu’s border, attacking at Yi, Qian and Liu. Chu’s army chased them, always arriving to find them gone. By 506 BCE Chu’s manpower and supplies were exhausted, its soldiers were worn out, and the court was at breaking point.

Two of those three years of exhaustion were enough to trigger the crisis. In 507 BCE the rulers of Cai (蔡) and Tang (唐) — whose king and duke had been held prisoner by Chu for three years and who had been systematically extorted by Nang Wa — broke with Chu and allied with Jin and Wu. In the spring of 506 BCE eighteen states met at Zhaoling to plan an attack on Chu, and in the autumn Chu besieged Cai. Wu now had both a cause and an excuse: relieving Cai.

The movement

The movement itself was the campaign. Wu’s army of some thirty thousand — the figure comes from the later tradition, not the early annal — put to sea and sailed up the Huai River, then turned to the Cai border. Chu was forced to lift the siege of Cai and pull back to defend its own territory. When Wu reached the Huai bend at Huai Rui, it abandoned the ships and marched overland instead.

That decision is the one the later tradition builds the whole campaign on, and it is attributed there to Sun Wu: the army was strong on water and weak on land, so it would move by the route the enemy did not expect, and speed was worth more than the advantage of the fleet. Wu took three thousand five hundred elite troops as a vanguard and pushed through the passes of Datun, Zhiyuan and Mingai into Chu from the north-east, reaching the east bank of the Han River (漢水) within days. The Han was the line: crossing it turned a raid into an invasion.

Chu took up position on the west bank, opposite them, with its prime minister Nang Wa (囊瓦), its Left Marshal Shen Yin Shu (沈尹戌) and the minister Shi Huang (史皇). Shen proposed the plan that would probably have won the war: Nang Wa should hold the main army on the Han while Shen went north to Fangcheng (方城) on Chu’s northern frontier, destroyed the Wu ships left on the Huai, and blocked the passes on Wu’s line of retreat. Then the two Chu forces would attack Wu from front and rear at once. It recognised something the plan that followed ignored: an army that cannot get home cannot be beaten, only released.

The plan was abandoned before it was executed, and two separate men argued for abandoning it. The general Wu Cheng Hei told Nang Wa that if they waited for Shen Yin Shu the credit would be Shen’s alone, and that Nang Wa’s own merit would then be in question. The minister Shi Huang added the sharper point: the people of Chu hated Nang Wa and loved Shen Yin Shu, so if Shen won first, Nang Wa would be ruined. Nang Wa changed his mind, ordered the army across the Han immediately, and attacked.

Wu did not stand and fight. It withdrew from the east bank of the Han, drawing Chu on, and met it at rest between Xiaobie (小別) and Dabie (大別). Three battles, three Wu victories. The Chu commander wanted to abandon the army and run; Shi Huang told him that losing the war was a capital offence and that the only way out was to fight it out. Nang Wa reformed his lines and drew up at Boju.

The annal for the year is one line — "on gengwu in the eleventh month, the two armies were drawn up at Boju" — and the battle that followed was short. Fugai (夫概), the king’s younger brother, asked Helü for permission to attack, arguing that Nang Wa was not a man of honour and that few Chu soldiers would fight to the death for him. Helü refused. Fugai took five thousand of his own men straight into the Chu camp, exactly as he had said they would break, and they broke. Shi Huang was killed. Nang Wa fled to Zheng.

What Wu did next was a habit rather than a pursuit. At the Qingfa River (清發水) Helü wanted to attack the fleeing army at once; Fugai advised waiting until they were half across, because a army caught at the ford cannot reform. The Chu rushed the crossing and were struck while strung out, and about half of them were captured. The survivors made it to the Yongshi (雍澨), where they were cooking their meal when Wu caught them; the Wu soldiers ate the meal and went on after them.

Shen Yin Shu was still coming. He had marched from Xi (息) to relieve Nang Wa, and his counterattack broke Fugai’s vanguard before the Wu main force came up and surrounded him. Shen fought, was wounded three times, and would not be taken alive, so he had his own head cut off and carried back to the Chu king. Wu then took the rest of the Chu army in a further series of engagements — five battles in all — and marched on the capital.

King Zhao of Chu heard the news at the front and fled, against the advice of his ministers, taking only his personal guard. The Chu army dissolved as it heard; Zi Qi took a detachment to guard the king and Zi Xi fled west with the remnants. On the twenty-ninth day of the eleventh month the Wu army entered Ying (郢都), the capital of Chu.

The decisive moment

The decision that decided the campaign was Nang Wa’s decision to abandon Shen Yin Shu’s plan and attack at once. It was made on an estimate of his own reputation rather than of the enemy, and it put Chu’s army across the river in a single push — where it could be defeated in detail, over and over, without ever being beaten in a single decisive action.

The second decision was Wu’s six-year strategy of wearing Chu down before striking at all. Three columns raiding the border so that Chu’s army was always marching and never fighting is an expensive way to spend six years, and it is exactly the protracted campaign the Art of War warns about. It worked anyway.

The third decision was Fugai’s. He asked, was refused, and attacked with five thousand men anyway. In the Zuo Zhuan this is simply a battle-leader’s reading of an enemy’s morale, and he was right. He then pushed on past the capital without waiting for the king, which is a different kind of decision and a much more dangerous one.

The fourth belonged to Wu Zixu, who entered Ying and had the corpse of King Ping of Chu dug up and whipped three hundred times. It was an act of revenge that would cost Wu politically, and it is the moment when Shen Baoxu (申包胥), a Chu minister, made his decision to go north to Qin.

The outcome

Wu had won every battle and lost the war. Chu’s capital was taken, its king was living in the smaller state of Sui, and its territory needed a foreign army to win back. Shen Baoxu, who had rebuked Wu Zixu for the desecration of the king’s tomb, refused to accept the king’s order of retreat and went to Qin unbidden. Duke Ai of Qin refused him; Shen Baoxu then stood in the Qin court and wept for seven days until the duke relented and sent an army, the later Chinese retelling putting it at five hundred war-chariots. In 505 BCE the Qin and Chu armies together defeated Wu in several battles.

And while Wu was deep in Chu, Yue attacked Wu’s own capital at Gusu from the south. Helü was forced to withdraw in September of that year, turning his back on the campaign he had won in order to save his state. Wu had taken a kingdom and lost the ability to leave the campaign. The state that had sacked Ying was itself destroyed by Yue in 473 BCE, thirty-three years later.

The Shiji puts the campaign inside Sun Tzu’s career. In the ninth year of Helü’s reign the king turned to Wu Zixu and Sun Wu: "Formerly, you declared that it was not yet possible for us to enter Ying. Is the time ripe now?" Their answer, as Giles translates it, was that Chu’s general Tzu-chang was grasping and covetous, and that the princes of Tang and Tsai both had a grudge against him; if the king had resolved on a grand attack, he must win over Tang and Tsai first, and then he might succeed. The Shiji also preserves Sun Wu at the earlier campaign of 512 BCE, telling the king: "The army is exhausted. It is not yet possible. We must wait."

What the record cannot tell us

The central unresolved question is not tactical but biographical. The Zuo Zhuan, the earliest narrative and by a long way the most detailed, names Helü, Fugai, Wu Zixu, Nang Wa, Shen Yin Shu and Shi Huang at Boju and does not mention Sun Wu. The Shiji, written around a century later, does. The Song-dynasty scholar Ye Shi was the first to notice the silence, and his judgement was that the Sun Wu material in the Shiji is close to legend — "too fantastical to be believed". Giles, translating the Shiji in 1910, called the story of Sun Wu’s career "the reckless fabrication of theorizing pundits" and the famous episode of the two hundred concubines "utterly preposterous and incredible", while still accepting that Sima Qian himself had no doubt about the existence of the man.

Two of the things most often repeated about Boju are not in the early record at all. The feigned retreat that the later Chinese retellings credit to Sun Wu — Wu withdrawing from the Han to wear Chu down before meeting it at Xiaobie and Dabie — appears in the Shiji-derived tradition and is not in the Zuo Zhuan’s account as it survives. So does the detachment of three thousand five hundred elite troops sent to seize the northern passes, and the famous exchange in which Wu Zixu asks why the army is marching by land and Sun Wu explains that speed is worth more than the advantage of the fleet. Both are in the tradition; neither is in the earliest source.

The troop numbers cannot bear the weight usually placed on them. The figures of thirty thousand Wu against two hundred thousand Chu come from Liu Hsiang, writing in the first century BCE, and are repeated by Giles; they are not independently corroborated, they are not the same order of magnitude as the other figures in the Zuo Zhuan, and no casualty count in the early account lets you test them. The Zuo Zhuan itself gives only one number of its own: the five thousand men Fugai led into the decisive attack.

The exact day is given in two incompatible ways, and the annal does not settle it. The Chunqiu entry for the year reads "on gengwu in the eleventh month, the two armies were drawn up at Boju"; later Chinese accounts convert that to the eighteenth day of the month, and the modern English summaries of the Zuo Zhuan give the nineteenth. The gap between Boju and the fall of Ying is given the same two ways — ten days in the Shiji-derived retelling, and eleven if you count from the eighteenth to the twenty-ninth of the month.

The location of the battle is not fixed. Three main candidates are on offer for Boju itself, and the Zuo Zhuan names Xiaobie, the Dabie Mountains, the Qingfa and the Yongshi without securely identifying any of them in modern geography. There is also no early account of how Ying itself was taken, what happened to the Wu fleet on the Huai, or how the passes Shen Yin Shu meant to block were actually held.

Finally, the text itself may postdate the campaign. The bamboo-slip Art of War found at Yinque Shan in 1972 was sealed in a pit between 134 and 118 BCE, and its content is about a third of the length of the received text. Most scholars have followed Ye Shi in assigning the received book to the beginning of the Warring States period — that is, to a century or more after Sun Wu. The passage usually quoted as Sun Tzu’s commentary on Boju, "Though according to my estimate the soldiers of Chu exceed our own in number, that shall advantage them nothing in the matter of victory… How victory may be produced for them out of the enemy’s own tactics — that is what the multitude cannot comprehend", is therefore later text applied backwards to the battle.