The Yellow Emperor and Chiyou waged a fierce battle, and after nine encounters, the Yellow Emperor had yet to win a single one. Desperate, the Yellow Emperor retreated to Mount Tai, where thick fog enveloped the area for three days and three nights. In a moment of despair, he knelt on the earth and prayed to Heaven for guidance. Suddenly, a divine figure descended from the heavens. She had the head of a woman and the body of a bird, stepping on a rainbow-colored cloud, surrounded by a dazzling aura of light. The Yellow Emperor, filled with awe, prostrated himself before her. The goddess spoke: “Compassionate Yellow Emperor, I am the Nine Heavens Xuan Nu. Do you have any questions for me?”
The Yellow Emperor replied, “Great Goddess, I wish to know how I can win every battle and how to set up ambushes without being detected by my enemies.”
The Xuan Nu then began to impart her knowledge of military strategy to the Yellow Emperor.
She said, “The key to military success lies in following the laws of heaven and earth. The laws of heaven are represented by the six Jiazi (a system of Chinese cyclical calendar), while the laws of earth are represented by the six Guiyou (another cyclical pattern). If you align your strategy with these laws, victory will be guaranteed.” Then, she drew a diagram of Yin and Yang for the Yellow Emperor and continued, “In battle, soldiers must be capable of fighting ten times their number. This ensures a basic guarantee of success, meaning human strength. Soldiers must also lead by example, taking the lead in battle, as this allows the army to command the spirits and achieve victory. If your enemy advances, know that this enemy has been victorious in previous battles, and their strength is formidable. To overcome them, we must adapt our formation accordingly. If the enemy forms a line, you must attack with a square formation. If they use a square formation, counter it with a pyramid-shaped attack. If they adopt a crescent shape, then you must use a circular formation to attack. If they employ a Dui (open) formation, then you should use a crescent formation to break through.”
The Xuan Nu also advised the Yellow Emperor on the tactics of troop movements, encampments, and defense strategies. She stressed the importance of boosting morale by using drums to rally the soldiers and taught him how to gauge the enemy’s strength by listening to the sounds of their drumming.
Armed with the Xuan Nu’s teachings, the Yellow Emperor’s army became highly adaptable, capable of adjusting its tactics to any situation. In addition, the Xuan Nu guided the Yellow Emperor to Mount Kunwu, where he discovered a red copper ore and used it to forge a magical sword. The sword, once forged, gleamed with a cold, bluish light, transparent like crystal and incredibly sharp.
With the Xuan Nu’s military strategy and the powerful sword in hand, the Yellow Emperor’s army grew confident. Despite Chiyou’s alliances with the Wind King, Rain Master, and the Miao people, Chiyou’s lack of wisdom and strategy led to his eventual defeat.
It is said that the Yin-Yang diagram, which the Xuan Nu had drawn for the Yellow Emperor, was hidden in a deep cave beneath Mount Kuaiji. The cave was said to be a thousand zhang deep (about 3,300 feet) and the diagram was wedged between two protruding stones. To retrieve it, one had to scale these perilous rocks, which hung over the deep abyss, resulting in many lives being lost in the process.
Legend has it that when Emperor Yu (Dayu) was controlling the floods, he learned about the diagram’s location and devised a plan to fill the cave with water. This would cause the dragons to float up, allowing him to retrieve the diagram. Emperor Yu released the floodwaters into the cave, and the dragon gods brought up the twelve volumes of the Yin-Yang diagram. However, as he was about to open it, four of the volumes flew up into the sky, and four others fell into the water. In the end, Emperor Yu only managed to recover the four middle volumes of the diagram.