The Battle of Changshao (Chinese: 長勺之戰) was a military conflict between Qi and Lu, two major principality states in the Shandong Peninsula during the Spring and Autumn period of the Zhou dynasty.

This battle is considered as a classic example of winning by good military strategies, and the well-known chengyu 一鼓作氣 (yī gŭ zuò qì, lit: "first drum creates spirit", explained below) was derived from Cao Gui's assessment of the battle, as recorded by the Zuozhuan.

[1] Cao Gui asked the army of Lu to stand still in the battle formation and fortifications and not to fight back until his order.

When the Qi soldiers started their third charge, Cao Gui ordered the army of Lu to launch a counterattack.

"[4] The direct quote, "the first drum raises spirits" (一鼓作氣) has become a chengyu (classical four-character idiom) that expresses the idea that one should aim to complete a difficult task by giving one's best, sustained effort on a favorable occasion when one is most encouraged and confident of success, rather than to waver in one's effort and have to try again on a future occasion, at which time one might well have lost confidence or enthusiasm.