Deception in War is Never Out of Place (Bing Bu Yan Zha)
During the reign of Emperor An of Han, the Qiang tribes frequently raided the borders of the Han dynasty. On one occasion, they even surrounded Wudu Commandery. Emperor An quickly appointed General Yu Xu to lead troops against the Qiang forces. Yu Xu and his men marched overnight toward Wudu, but upon reaching the area of Chen Cang and Xiao Valley, they were blocked by a large Qiang army.