In the beginning of the world, before the gods came to dwell in Olympus, all the universe was in the hands of the Titans; and among these the greatest was Saturn,--or Cronos,[39]--who wedded his sister Rhea (also called Cybele) and became the father of three sons and three daughters, Jupiter, Pluto, Neptune, Ceres, Vesta, and Juno. For many ages Saturn and Rhea, having subdued all the opposing Titans, ruled over heaven and earth; but when the cruelty of Saturn drove his children into rebellion, there arose a mighty war in the universe, in which the sons and daughters of Saturn leagued against their father, who had called upon the other Titans for aid. After years of combat the six brothers and sisters, helped by the Cyclops,[40] defeated the allied Titans and imprisoned them in the black abyss of Tartarus--all except a few who had not joined in the war against the children of Saturn. Among those who were wise enough to accept the new sovereignty were Mnemosyne (Memory) and Themis, goddess of justice. Those descendants of the Titans who refused to acknowledge the supremacy of Jupiter were consigned to the center of Mount Etna, and were the giants who constantly turned over and over, making Pluto fear for the safety of his realm. A few of the giants were spared: Atlas, whose punishment was to hold the heavens on his shoulders, and Prometheus and Epimetheus who had espoused the cause of Jupiter and so escaped the fate of the conquered Titans. When the children of Saturn found themselves masters of the world, they agreed to accept Jupiter as their ruler, on condition that the two other brothers be given a share in the universe. So a division was made whereby Pluto became king of the underworld--or Hades; Neptune took the dominion of the sea; and Jupiter, having married his sister, Juno, established his dwelling in Olympus as lord of heaven and earth. The kingdom of Pluto[41] was dreaded by all mortals, and its ruler inspired men with great fear. Though Pluto was known to visit the earth from time to time, no one wished to see his face, and each man dreaded the moment when he should be obliged to appear before the grim monarch of Hades, and be assigned a place among the innumerable dead. No temples were dedicated to Pluto, though altars were sometimes erected on which men burned sacrifices to this inexorable god while petitioning him to be merciful to the souls of the departed. The festivals held in his honor were celebrated only once in a hundred years, and on these occasions none but black animals were killed for the sacrifice.