Legend has it that in prehistoric times the Jade Emperor held a race to see which animals would be first to cross a river. The first 12 animals would, according to order, represent the combinations of celestial stems and terrestrial branches. These animal symbols would help mankind to better keep track of the years.
相傳上古時代，玉皇大帝決定在他生日那天，舉辦動物渡河競賽，最先抵達終點的十二種動物，將依序代表天干地支，以便人類記算年序時歲。