remembered as both the opponent and doublet of Erechtheus, the first king of Athens. Erechtheus was given a hero-cult at his tomb under the title Poseidon Erechtheus. In another possible echo of this archaic association, the chief ritual of Atlantis, according to Plato's Critias, was a nocturnal horse-sacrifice offered to Poseidon by the kings of the imagined island power. In keeping with the mythic equation between horsemanship and seamanship, the equestrian heroes Castor and Pollux were invoked by sailors against shipwreck. Ancient Greeks interpreted the phenomenon now called St. Elmo's Fire as the visible presence of the two brothers. Old men and nymphs Several types of water deities conform to a single type: that of Homer's halios geron or Old Man of the Sea: Nereus, Proteus, Glaucus and Phorkys. These water deities are not as powerful as Poseidon, the main god of the oceans and seas. Each is a shape-shifter, a prophet, and the father of either radiantly beautiful nymphs or hideous monsters (or both, in the case of Phorkys). Nymphs and monsters blur, for Hesiod relates that Phorcys was wed to the "beautiful-cheeked" Ceto, whose name is merely the feminine of the monstrous Cetus, to whom Andromeda was due to be sacrificed. Each appearance in myth tends to emphasize a different aspect of the archetype: Proteus and Nereus as shape-shifters and tricksters, Phorcys as a father of monsters, Nereus and Glaucus for truth-telling, Nereus for the beauty of his daughters. Each one of these Old Men is the father or grandfather of many nymphs and/or monsters, who often bear names that are either metaphorical (Thetis, "establishment"; Telesto, "success") or geographical (Rhode from "Rhodes"; Nilos, "Nile"). Each cluster of Old Man and daughters is therefore a kind of pantheon in miniature, each one a different possible configuration of the spiritual, moral and physical world writ small - and writ around the sea. The tantalizing figure of the halios geron has been a favorite of scholarship. The Old Men have been seen as everything from survivals of old Aegean gods who presided over the waves before Poseidon (Kerenyi) to embodiments of archaic speculation on the relation of truth to cunning intelligence (Detienne). Homer's Odyssey contains a haunting description of a cave of the Nereids on Ithaca, close by a harbor sacred to Phorcys. The Neoplatonist philosopher Porphyry read this passage as an allegory of the whole universe - and he may