According to the Great Race legend, the Ox arrived first but lost the top place to the Rat.
In one popular version of the story, the Ox agrees to carry the Rat across a river. Near the finish, the Rat jumps ahead and reaches the Jade Emperor first, while the Ox comes second. The tale explains why Rat begins the traditional twelve-animal sequence and Ox follows it.
The race is a folklore explanation, not the historical origin of the zodiac system. Chinese calendrical traditions involving earthly branches are much older and developed through complex religious, astronomical, and administrative practices. Different retellings change details, including how the animals cross the river and whether the Rat deliberately deceives the Ox.
The story remains influential because it gives a memorable narrative order to the animals. It also explains personality stereotypes often attached to Rat and Ox in popular zodiac writing.