The Battle of Tong Pass, also known as the Battle of Weinan, was fought between the warlord Cao Cao and a coalition of forces from Guanxi between April and November 211 in the late Eastern Han dynasty of China. The battle was initiated by Cao Cao's western expansion, which triggered uprisings in Guanxi. Cao Cao scored a decisive victory over the Guanxi coalition and established a hold of the Guanzhong region.
Background
Towards the end of the Eastern Han dynasty, the warlord Ma Teng commanded a sizable army in the northwestern frontiers of China that threatened the North China Plain under the dominion of Cao Cao. When Cao Cao finished his unification of northern China in 207, he wished to turn south to attack the warlords Liu Bei and Sun Quan. To avoid a potential attack from behind, Cao Cao appointed Ma Teng as an official and summoned him to Ye. Ma Teng and some of his family members were effectively held hostage to prevent Ma Teng's son, Ma Chao, from invading Cao Cao's territory.
Cao Cao's southern expedition failed and he was defeated by the combined forces of Sun Quan and Liu Bei at the Battle of Red Cliffs in 208. He turned his attention west instead and prepared to invade the Guanzhong region.
In April 211, Cao Cao ordered Zhong Yao to lead an army against the warlord Zhang Lu in Hanzhong Commandery and sent Xiahou Yuan at the head of another force from Hedong Commandery to support Zhong Yao. Gao Rou cautioned Cao Cao against such a move, saying that sending troops west could draw suspicion from the warlords in the area and cause them to revolt.
The various warlords in the Guanzhong region feared that Cao Cao would to attack them because Zhong Yao's army would pass by the Guanzhong region on the way to Hanzhong Commandery. As soon as Zhong Yao's army entered Guanzhong, the warlords, under the leadership of Ma Chao and Han Sui, formed a coalition and rebelled against the Han imperial court. The warlords included Hou Xuan (侯選), Cheng Yin (程銀), Yang Qiu, Li Kan (李堪), Zhang Heng (張橫), Liang Xing (梁興), Cheng Yi (成宜), and Ma Wan (馬玩). The coalition comprised a mixture of Han Chinese, Qiang, and Hu soldiers. Many counties in the area joined the uprising. Some civilians escaped to Hanzhong via Ziwu Valley (子午谷) to avoid the war.
In response, Cao Cao sent Cao Ren against the coalition at Tong Pass (in present-day Tongguan County, Shaanxi) and gave strict orders to his generals to refrain from engaging the enemy.
Crossing of the Wei River
In late July or August 211, Cao Cao personally led an army against the rebels; he probably left behind his son Cao Pi to guard his base in Ye (in present-day Handan, Hebei). Some of his subordinates advised him: "The Guanxi soldiers are warlike and they specialise in using long spears. Only an elite vanguard force can stop them." Cao Cao replied: "I am in charge of the war, not the rebels. They may be skilled in using long spears, but I will make them unable to use their spears. Gentlemen, just watch."
Upon reaching Tong Pass, Cao Cao ordered Xu Huang and Zhu Ling to lead their units across the Wei River via Puban Ford (蒲阪津) at night and set up a camp on the west bank. While Cao Cao and his men were preparing to cross the Wei River to the north bank, they suddenly came under attack by Ma Chao's forces, but Cao remained seated and refused to move. Zhang He and the other officers saw that the situation was very critical, so they led Cao Cao on board a ferry. As the river current was very strong, Cao Cao's vessels quickly sailed four or five li away from the south bank. Ma Chao ordered his troops to rain arrows upon the enemy boats. Ding Fei (丁斐), a colonel under Cao Cao, had released the cattle and horses to distract the enemy, so the Guanxi soldiers immediately gave up on attacking and started to seize whatever livestock they could lay their hands on. Cao Cao's officers were worried and panicky when they lost sight of their lord during the chaos, and they shed tears of joy when they reunited with him later. Cao Cao laughed and remarked: "I was almost trapped by that little scoundrel today!"
Construction of sand walls
After crossing the river, Cao Cao and his forces then headed south along the riverbank. The coalition retreated and made camp along the Wei River. Cao Cao set up many decoys to confuse the enemy while secretly sending troops to sail across the river and construct pontoon bridges. His forces crossed the river that night and built camps on the south bank. On the same night, the coalition attacked but were driven back by ambush forces deployed earlier by Cao Cao. Ma Chao and his allies also garrisoned at the south bank and they sent a messenger to meet Cao Cao, requesting to give up the territories west of the river in exchange for peace, but Cao Cao refused.
In late October or November 211, Cao Cao's forces attempted to cross the Wei River again, but came under attack by Ma Chao and his cavalry each time they tried to cross. Their camps were not stable and they could not build ramparts because the terrain was too sandy. Lou Gui suggested to Cao Cao: "The weather is cold. We can mix sand with water and use the mixture to construct walls. They will be ready after one night." Cao Cao heeded Lou Gui's suggestion and ordered his troops to work through the night to build the walls, which were ready by the following day. Cao Cao and his forces were hence able to cross the Wei River while the enemy was kept at bay by the walls. Ma Chao led his men to attack the walls but were repelled by Cao Cao's ambushes.
However, there have been suspicions that the building of the sand walls did not actually occur, because the incident took place in late autumn or early winter (late October to November) and the weather was probably not cold enough to cause water to freeze. The fifth-century historian Pei Songzhi commented that the Wei Shu stated that Cao Cao's army reached Tong Pass in late August or September 211, and crossed the Wei River to the north bank in late September or October. The weather could not possibly be that cold in late autumn (late September to October) to cause water to freeze.
Cao Cao sowing discord between the coalition members
Ma Chao and the coalition repeatedly challenged Cao Cao to come out and engage them in battle but Cao ignored them. The rebels then offered to cede territories and send a hostage to Cao Cao's side in exchange for peace. As suggested by Jia Xu, Cao Cao pretended to agree to accept their offer.
Han Sui had a meeting with Cao Cao later. Han Sui's father and Cao Cao were nominated as xiaolian (civil service candidates) in the same year, while Cao and Han were also former colleagues when they were working in the old capital Luoyang. When they met at close quarters, they spoke nothing about military affairs and had a mere lighthearted conversation about old times. When Han Sui returned to his camp later, Ma Chao asked him: "What did Cao Cao say?" Han Sui replied: "Nothing." Ma Chao and the others became suspicious of Han Sui.
When Cao Cao was going to meet Han Sui again later, his subordinates cautioned him: "My lord, when you meet the rebels, you may not be able to leave easily. How about using wooden horses as barriers?" Cao Cao agreed to their suggestion and spoke to Han Sui and his allies from behind the barriers. The coalition members greeted Cao Cao when they met him while their soldiers pushed their way forward to get a closer look at him. Cao Cao laughed and said: "You wish to see how I look like? I am also an ordinary person. I don't have four eyes or two mouths, but I am more intelligent." Cao Cao had brought along 5,000 armoured horsemen and instructed them to arrange themselves in an impressive formation. The rebel forces were shocked when they saw this display of military might by Cao Cao.
Some days later, Cao Cao wrote a letter to Han Sui which contained several "amendments", making it seem as though the recipient had deliberately edited the letter's contents to cover up something. Ma Chao and the others became even more suspicious of Han Sui after they saw the letter. In the meantime, Cao Cao was preparing for war with the coalition. He sent lightly armed troops to attack first, and then dispatched his elite cavalry to launch a pincer attack. Cao Cao scored a major victory over the coalition: Cheng Yi, Li Kan, and others were killed in action; Yang Qiu fled to Anding Commandery (安定郡; around present-day Pingliang, Gansu); Ma Chao and Han Sui retreated back to Liang Province. The Guanzhong region was pacified.
Aftermath
In late November or December 211, Cao Cao led an army from Chang'an to attack Yang Qiu and his forces besieged Anding Commandery (安定郡; around present-day Pingliang, Gansu). Yang Qiu surrendered and was allowed to retain his former titles and remain in his domain to pacify the people there.
Ma Chao retreated further west after his defeat at Tong Pass. Cao Cao pursued him to Anding Commandery but gave up on the pursuit after two months and headed back to Ye (in present-day Handan, Hebei) upon receiving news about unrest in northern China. He left Xiahou Yuan behind to defend Chang'an.
About a year after Ma Chao rebelled against the Han imperial court, Emperor Xian issued a decree ordering the execution of Ma Chao's family members in Ye.
After Cao Cao left, Ma Chao led the various tribes in the region to attack the commanderies and counties in Guanzhong, while the people responded to his call and joined him in the revolt. In 213, Ma Chao killed Wei Kang, the Inspector of Liang Province, seized control of Jicheng (兾城) and forced Wei Kang's subordinates to submit to him. He took control of Liang Province. Wei Kang's former subordinates were unhappy with Ma Chao so they plotted to get rid of him. Later that year, they rebelled against him and succeeded in driving him out of Guanzhong.
Ma Chao fled to Hanzhong, where he borrowed troops from the warlord Zhang Lu, and returned to attack those who drove him out of Guanzhong. He besieged Jiang Xu, Zhao Ang, Wang Yi, and their allies at Mount Qi (祁山; the mountainous areas around present-day Li County, Gansu) for about 30 days until reinforcements led by Cao Cao's generals Xiahou Yuan and Zhang He showed up and lifted the siege.
Cao Cao's analysis of the battle
After the battle, Cao Cao's officers asked their lord: "Earlier on, when the rebels were at Tong Pass, the north of the Wei River was not guarded. Why didn't you attack Pingyi (馮翊) from the east bank, and instead choose to defend Tong Pass and cross the river later?" Cao Cao replied, "The rebels were at Tong Pass. If I went to the east bank, they would definitely increase their defences at the fords and we wouldn't be able to cross over to the west. Hence, I chose to deploy our forces at Tong Pass so that the rebels would concentrate their defences on the south bank and lower their guard in the west. This was why our two generals were able to capture the west bank first, after which our main army crossed over to the north bank. The rebels were unable to fight for control of the west bank with us because our two generals had already occupied the area. When I gave orders for our carts to be linked together, wooden fences to be erected as defensive structures, and for our army to head south along the riverbank, I knew that we couldn't win then so I decided to display our weakness to the enemy. When we crossed the river back to the south bank and built solid walls, I didn't allow our men to engage the enemy because I wanted the enemy to become overconfident. As such, the rebels didn't attack our walls and instead requested to cede territories in exchange for peace. I pretended to agree so that they would be at ease and would not be on guard while our troops prepared for battle. When we attacked, it was indeed a case of 'a sudden crash of thunder leaves no time for one to cover his ears'. There are more than one way to how the situation on a battlefield can change."