Chinese system of Astrology indicates the year of birth according to a certain phase or aspect of a sixty-year cycle of time. It implements three systems for counting and categorizing the years. They are- The ten Heavenly Stems, the twelve Earthly Branches and the twelve Animals. However the exact origins of the twelve animal systems remain unknown but the legend goes that-
Once upon a time, the Jade King had nothing to do in Heaven and he felt uninterested. His work on Earth was being looked after by his servants, so he had no work to take care of. He decided that he wanted to see the animals that inhabited the earth so he asked his advisors to bring him twelve animals of good breed. The advisor first sent an invitation to the Rat, telling him to also bring the cat. The Rat, out of jealousy, didn’t extended King’s invitation to cat.
Additional invitations were sent on to the Ox, the Tiger, the Rabbit, the Dragon, the Snake, the Horse, the Ram, the Monkey, the Rooster and the Dog, asking them to be present at the palace the next day. On their presence, the king found that there were only eleven animals instead of twelve, as he had called for. The king sent his servant down to Earth to get back a twelfth animal. The servant came across a man carrying a Pig, and he, in a hurry, snatched it and delivered it to the king.
The animals stood in front of the king in no particular order. The Rat, being smaller than the rest, hopped on the Ox's back and proceeded to play the flute. The king was very impressed by this display. He gave the Rat first place. Second place was given to the Ox for its good sportsmanship, and third was given to the Tiger, who appeared so courageous. The Rabbit was given fourth place, the Dragon fifth, the Snake sixth, the Horse seventh, the Ram eighth, the Monkey ninth, the Rooster tenth and the Dog eleventh. By default, and due to the king's just nature, twelfth place went to the Pig. After the ceremony got finished, the cat, who had missed the invitation, begged the king to reconsider. He was told it was too late.