Following the philosophical thought of Plato (427-347 BC), Eudoxus of Cnidus (4th century BC) believed that the planets orbited in a uniform circular path around the immobile Earth. Jupiter, for example, followed a path governed by four spheres concentric to the Earth, pivoting on one another. The outermost sphere governed the daily rising and setting of the planet. The next one governed the mean motion of Jupiter along the zodiac. The two innermost spheres, instead, accounted for the fact that the planet, as seen from the Earth, appeared to stop periodically and move backward against the starry background.