Mnemosyne — Classical Greek Myth Library

In Arcadian tradition, while Demeter searched for Persephone, Poseidon pursued her. At Thelpusa she transformed herself into a mare and mingled with the horses of Oncius; Poseidon likewise became a stallion and covered her. From that union Demeter bore a daughter—called only Despoina (“Mistress”) in the mysteries, her true name reserved for initiates—and the divine horse Areion (Arion), black-maned and gifted with speech in some tellings. Demeter, angry at the rape, put on black clothing and shut herself in a cave; the Arcadians called her Demeter Melaina (Black Demeter). Pausanias describes her cult image at Phigalia/Thelpusa with a horse’s head, and at Lycosura the sanctuary of Despoina shared with Demeter, where the Mysteries of the Mistress were celebrated. Areion later became the horse of Heracles or of Adrastus: Apollodorus notes that Adrastus alone escaped the disaster of the Seven against Thebes on Areion’s back. The myth thus joins Olympian genealogy (Poseidon–Demeter) to Arcadian horse cult and to the epic horse that saves Adrastus—local mystery and panhellenic saga in one strand.