The planet was Ninurta in Mesopotamia and was identified with the Greek Kronos, the Titan who devoured his children and was overthrown by Zeus, and with the Roman Saturn, an agricultural god of the sown seed whose December festival, the Saturnalia, inverted the social order for its duration and left traces in later midwinter custom. In India the planet is Shani, feared and propitiated, the significator of hardship, discipline and the results of past action. Saturn also carried the Greek and later medieval association with the melancholic humour of black bile, and it was through the Renaissance reading of Aristotle's Problemata by Marsilio Ficino that the melancholic Saturnine temperament was reinterpreted as the mark of the contemplative and creative genius, an idea traced in detail by Klibansky, Panofsky and Saxl. The rings, invisible to the ancients, were first seen by Galileo in 1610 and correctly described by Huygens in 1655.
Two periods give Saturn its structural role. Its orbit takes about 29.5 years, so it returns to its natal place at about twenty nine or thirty and again at about fifty nine, the intervals modern astrology calls the Saturn return and the older literature marks as the thresholds of maturity and of age. And Jupiter and Saturn, the two slowest visible planets, conjoin about every twenty years, the great conjunction on which the medieval theory of historical periods was built. Saturn was also the outermost body anybody could see, so the classical scheme placed it at the boundary of the cosmos, and its significations of limit, ending, structure and the outer edge of what can be reached follow from where it sits as much as from any myth.