Around 480 B.C., during the late Spring and Autumn Period, King Fu Chai of Wu had conquered Yue, Lu, and Qi. Ambitious to expand further, he led his army northwest to attack the State of Jin.
Meanwhile, King Gou Jian of Yue launched a surprise attack on Wu's rear, capturing its capital, Gusu, seizing its large boats, and occupying the Huai River to cut off Fu Chai's retreat.
Upon receiving this shocking news, Fu Chai urgently consulted his advisors. They concluded that retreating would mean certain defeat, caught between Jin and Yue. Their best chance was a swift, surprise victory over Jin first.
To achieve this, Fu Chai organized a special night assault. He selected 30,000 elite troops, dividing them into three phalanxes of 10,000, each distinguished by color:
- The central phalanx, led by Fu Chai himself, wore white armor and carried white flags and bows.
- The left phalanx wore red armor and carried red flags and bows.
- The right phalanx wore black armor and carried black flags and bows.
After a midnight march, the Wu army positioned itself near the Jin camp at dawn. As day broke, they beat their drums thunderously and raised a mighty shout.
The Jin soldiers, awakened from sleep, were stunned by the sight. The white phalanx looked like a field of flowering reeds, the red one like a raging fire, and the black one like an unfathomably deep sea.