Heavenly Stems&Earthly Branches
Because treachery had taken root and demons and monsters had appeared, the rebellion of Chi You arose in the age of the Yellow Emperor. Grieved by the tribulations of the people, the Yellow Emperor went forth to do battle with Chi You in the wilds of Zhuolu. Yet although the bloodshed stretched for a hundred li, he could not subdue him. It was at this time that the Yellow Emperor set about forging weapons — swords, shields, and halberds.
Fasting and purifying himself, the Yellow Emperor raised an altar and, on the day of the summer solstice, offered sacrifice to Heaven and Earth. Heaven, moved by his sincerity, sent down the Ten Heavenly Stems, which signify Heaven — namely Jia, Yi, Bing, Ding, Wu, Ji, Geng, Xin, Ren, and Gui — and likewise the Twelve Earthly Branches, which signify Earth — namely Zi, Chou, Yin, Mao, Chen, Si, Wu, Wei, Shen, You, Xu, and Hai. The Yellow Emperor arranged the Ten Heavenly Stems in a circle to mirror the round form of Heaven, and the Twelve Earthly Branches in a square to mirror the square form of Earth. From this, the Heavenly Stems came to stand for Heaven and the Earthly Branches for Earth; once the two were joined, each fulfilling its proper function, they could be employed to bring order to the realm. Such was the origin of the Ten Heavenly Stems and the Twelve Earthly Branches.
Later, Da Nao feared that future generations would be beset by the same affliction. "Alas!" he said. "The Yellow Emperor was a sage, and even he could not subdue and punish the wicked. Should the people once again meet with calamity and hardship, what recourse would they have?" He therefore paired the Ten Heavenly Stems with the Twelve Earthly Branches, one by one, to form the sexagenary cycle。 The order of the Heavenly Stems is: Jia → Yi → Bing → Ding → Wu → Ji → Geng → Xin → Ren → Gui.
As to their yin–yang nature: Jia, Bing, Wu, Geng, and Ren are yang, while Yi, Ding, Ji, Xin, and Gui are yin.
Jia and Yi belong to Wood in the Five Elements and are positioned in the East; Yin, Mao, and Chen also belong to the East, forming the image of the Azure Dragon.
Bing and Ding belong to Fire and are positioned in the South; Si, Wu, and Wei also belong to the South, forming the image of the Vermilion Bird.
Geng and Xin belong to Metal and are positioned in the West; Shen, You, and Xu also belong to the West, forming the image of the White Tiger.
Ren and Gui belong to Water and are positioned in the North; Hai, Zi, and Chou also belong to the North, forming the image of the Black Tortoise.
Wu and Ji belong to Earth and are positioned at the Center; Chen, Xu, Chou, and Wei also belong to the Center, forming the images of Goutian (the Hooked Array) and Tengshe (the Flying Serpent).
The god of the East is Taihao. He rides the "Zhen chariot" to symbolize thunder and lightning, presides over the ordering of the growth of all things, and governs the spring of the year. Benevolent winds and harmonious qi arise from it; plants and trees sprout from it. This is why Wood resides in the East — and so the heavenly stems Jia and Yi, together with the earthly branches Yin and Mao, are ranked in the East.
The god of the South is Shennong, the Divine Farmer. He rides the "Li chariot" to symbolize raging fire, presides over the ordering of the nurturing and growth of all things, and governs summer. Blazing sun and intense qi come forth from it; all things reach full growth by it. This is why Fire resides in the South — and so the stems Bing and Ding, together with the branches Si and Wu, are ranked in the South.
The god of the West is Shaohao. He rides the "Dui chariot" to symbolize the qi of Metal, presides over the ordering of the harvest of all things, and governs autumn. The killing, withering qi arises from it; plants and trees wither by it. This is why Metal resides in the West — and so the stems Geng and Xin, together with the branches Shen and You, are ranked in the West. Autumn's Five-Element affiliation with Metal is precisely because the autumn qi is like a blade, charged with a killing force that makes plants and trees fall; by this time all things are already ripe and no longer grow.
The god of the North is Zhuanxu. He rides the "Kan chariot" to symbolize the virtue of Water, presides over the ordering of the closing away and storing up of all things, and governs winter. Water vapor condenses into ice and snow from it; all things lie dormant and hidden by it. This is why Water resides in the North — and so the stems Ren and Gui, together with the branches Hai and Zi, are ranked in the North.
The god of the Center is the Yellow Emperor. He rides the "Kun chariot" to symbolize the great Earth, and governs the central Earth. The Wood, Fire, Metal, and Water of the four seasons and four directions cannot do without Earth; therefore the stems Wu and Ji reside at the center, while the branches Chen, Xu, Chou, and Wei are distributed among the four corners, each in its proper place. The "four corners" are the third month of spring, the sixth month of summer, the ninth month of autumn, and the twelfth month of winter.
In ancient times, the Grand Historian Da Nao established this system: among the Ten Heavenly Stems, Jia and Yi belong to Wood, Bing and Ding to Fire, Wu and Ji to Earth, Geng and Xin to Metal, and Ren and Gui to Water. Among the Twelve Earthly Branches, Yin and Mao belong to Wood, Si and Wu to Fire, Shen and You to Metal, Hai and Zi to Water, and Chen, Xu, Chou, and Wei to Earth.
Wood without Earth would lose the foundation of its cultivation and planting; Fire without Earth could not shine upon the four directions like a lamp; Metal without Earth could not put forth its keen edge; Water without Earth could not hold back the flooding waves like a dike. And Earth without Water could likewise not give life to and nourish all things. Thus it is evident that the Five Elements generate and sustain one another, and none can be dispensed with — this is why Earth is indispensable to all of them. Viewed as a whole, Earth resides at the center, while the Earth-attached branches are distributed among the four corners; and in this way the principle of the Five Elements — Metal, Wood, Water, Fire, and Earth — is established.