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 (west of Tong Pass) 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 (in present-day Handan, Hebei). 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.
Around 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 (known as the "Guanxi Coalition", or "coalition from the west of Tong Pass") and rebelled against the Han imperial court. The warlords included Hou Xuan (), Cheng Yin (), Yang Qiu, Li Kan (), Zhang Heng (), Liang Xing (), Cheng Yi (), and Ma Wan (). 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 () 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, leaving 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 () 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 (), 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!"