Based on an ancient agricultural calendar, the system is based on the influences of the different forces. Although the exact origins remain a mystery, legends abound on how it came to be.

One has it that on one of his birthdays, Yuhuang Dadi (the Jade Emperor of Heaven) invited all the animals on earth and heaven to join in the celebrations. But only 12 turned up and the party animals were Rat, Ox, Tiger, Rabbit, Dragon, Snake, Horse, Goat, Monkey, Rooster, Dog and Pig.

For their effort, the Emperor honoured each animal with a year of its own. It was also decreed that henceforth, those born in the year of the animal would assume the nature and characteristics of that animal influenced by the different elements.

And if you are wondering why Rat became the first animal in the zodiac? Well, Ox was in fact first but Rat, clever animal that it was, laid a bet with Ox. Sitting on Ox's head, Rat said "Let us take a walk around these heavenly grounds and see who will emerge as the 'big' animal."

Good-naturedly, Ox agreed.

"Oh, what a big, awful-looking rat," screamed one of the fairies and shook her head in disgust.

"See, I told you. Even fairies think I am 'big'!" declared Rat to Ox.

No arguments there and the tolerant Ox conceded.

Now why is there no cat in the line-up? Well, in those heavenly days, Cat and Rat were good friends. They both received the invitation to the birthday party but Cat was lazy and decided to ask Rat to reserve a place for him, while he stole a couple more hours of sleep.

"No problem," said Rat and off he went.

At Heaven, Rat got into a game with Ox and duly forgot his promise to Cat. When he returned, triumphant, Cat woke up to the rude reality that he was forgotten. Cat, of course, never forgave Rat. By the way, that's also why cats always catch rats.