The bull is among the oldest recognisable figures in the sky. It is MUL GU-AN-NA, the Bull of Heaven, in the Mesopotamian lists, the same creature Ishtar sends against Gilgamesh, and the constellation carries two of the most conspicuous star clusters visible without a telescope: the Hyades, the V of the bull's face with red Aldebaran at one horn, and the Pleiades, whose heliacal rising was used to set the agricultural year across the ancient Mediterranean and far beyond it. In Greek myth the bull is Zeus in the form he took to carry Europa across the sea to Crete. The prominence of the Pleiades is one reason this stretch of sky is marked in so many independent traditions, and it should not be assumed that all such traditions are related; several arrived at a cluster-based calendar independently, because the cluster is simply very noticeable.
Chou, the Ox's own branch, sits second in the fixed cycle of twelve and belongs, like yin the Tiger and hai the Pig, to no san he triad shared with the Bull-of-Heaven myth discussed above; the Mesopotamian and Chinese bull traditions developed in complete isolation from one another; there is no documented route of transmission between the Bull of Heaven that Ishtar sends against Gilgamesh and the ox that pulls the Chinese farmer's plough, and the resemblance is best read as two agrarian societies independently making a working animal into a major sky figure rather than as evidence of contact.