Ao, the giant turtle in Nüwa’s sky-repairing myth, had four legs that she cut off to support the sky.
The story begins after Gong Gong, a destructive water deity, damages Mount Buzhou, one of the pillars supporting Heaven. The collision causes the sky to tilt and the earth to break apart, bringing floods, fires, and other disasters. Nüwa, the creator goddess, repairs the damaged cosmos using extraordinary materials and divine actions.
Among her measures, Nüwa cuts off the four legs of Ao, a gigantic sea turtle, and uses them as supports for the sky. The four legs fit the myth’s directional structure: they function as replacement pillars stabilizing the heavens. This is why the answer is four rather than the eight limbs associated with some other giant or cosmic creatures.
Ao appears elsewhere in Chinese mythology as a world-bearing turtle. In another tradition, he carries the islands of the Eight Immortals on his back. Later Chinese art also connected the turtle-dragon Bixi with enormous strength and the carrying of heavy stone monuments. Those separate traditions can make the details seem interchangeable, but Nüwa’s repair story specifically names Ao’s four legs.