Battle of Chengpu

The Battle of Chengpu took place in 632 BC between the State of Jin and the State of Chu and its allies during the Spring and Autumn period of Chinese history. It was the first major battle in the protracted conflict between the states of the Yellow River valley, and the states of the Yangtze River valley. The Jin victory confirmed the hegemony of Duke Wen and checked Chu ambitions in the north for a period.

Following the death of Duke Huan of Qi in 643 BC, the state of Chu steadily extended its influence northward, absorbing half a dozen smaller states as its satellites. In 636 BC, Chong'er, a ducal prince of Jin, after nineteen years in exile traveling throughout numerous states, came to power as Duke Wen of Jin with the help of Duke Mu of Qin. Duke Wen assumed a position of leadership among the states and instituted numerous domestic reforms.

In the years leading up to 632 BC, conflict between Jin and Chu became increasingly public and was characterized by frequent shifts in alliances between the various small states that lay in a narrow band of land between the two larger states.

King Cheng of Chu attacked the State of Song, the ally of Jin most accessible from the south, in the winter of 633 BCE. In retaliation, an expeditionary force under Duke Wen marched south in the spring of the following year and occupied the States of Wey and Cao, both satellites of Chu. The two sides sought out alliances in the following months. The States of Shen, Xi, Chen and Cai, all immediately contiguous to Chu, sided with King Cheng, as well as the more distant State of Lu.

As promised by Duke Wen to King Cheng during his exile in Chu, the Jin army retired "three days march" (退避三舍) (45 km) before camping on the plain of Chengpu on the border of Wey and Cao, awaiting a decisive battle. The retirement also linked the Jin forces up with Qi and Qin reinforcements.

Only the central force of the Chu under Prime Minister Ziyu (子玉) was made up entirely of Chu troops. The left wing under Zixi incorporated soldiers from Chu's close satellites Shen and Xi. The right wing under Zishang comprised completely a separate detachment from the armies of Chen and Cai, perhaps numbering around a third of the entire force.

The Jin force was expanded before the expedition from two armies into three: the upper, the central and the lower; these three were then regrouped into wings before the battle: the upper army at the right wing under commander Hu Mao and vice-commander Hu Yan, lower at left under Luan Zhi and vice Xu Chen , central remained at center under Xian Zhen and vice Xi Chen . Duke Wen did not direct or engage in the fighting.

On the fourth day of the fourth month of 632 BC, the rival forces met.