There were already zodiac signs in the Western Han Dynasty, but it was not until the Eastern Han Dynasty that the twelve zodiac signs were completed.
The twelve zodiac signs were first seen in the "Book of Songs", the world's first collection of poetry. "The Book of Songs·Xiaoya·Che Gong" says: "On the auspicious day of Gengwu, I sent my horse." Also found in "Book of Rites, Yue Ling, Ji Dong": "The ox was unearthed to send away the cold air."
When did the theory of the twelve zodiac animals come into being? Some historical data say: it should have been formed in the Han Dynasty at the latest. The basis is based on the words of Wang Chong of the Eastern Han Dynasty in "Lunheng·Mao Shi Chapter": "Yin means wood, and its birds are tigers. Xu means soil, and its birds are dogs." Another saying goes: "Wu means horse. Zi means rat. You means chicken. ... Shen means monkey." *** proposed eleven zodiac names. In addition, in the "Wuyue Chunqiu" written by Zhao Ye of the Eastern Han Dynasty, there is "Wu Zaichen, whose position is dragon". Just add "Chen Long" to complete the twelve zodiac signs. It can be seen that the twelve zodiac signs have been formed in the Eastern Han Dynasty. As for the use of the twelve zodiac signs, it has appeared at least in the Northern and Southern Dynasties.