Poseidon
Arcadian myths

In the Arcadian myths, Poseidon is related to Demeter and Despoina (another name of Kore- Persephone) and he was worshipped with the surname Hippios in many Arcadian cities. At Thelpusa and Phigalia there were sister worships which are very important for the study of primitive religions. In these cults Demeter and Poseidon were chthonic divinities of the underworld.

Near Thelpusa the river Ladon descended to the sunctuary of Demeter Erinys (Demeter-Fury). During her wandering in search of her daughter Demeter changed into a mare to avoid Poseidon. Poseidon took the form of a stallion and after their mating she gave birth to a daughter whose name was not allowed to be told to the unitiated and a horse called Arion (very swift). Her daughter obviously had the shape of a mare too. At first Demeter became angry and she was given the surname Erinys (fury) by the Thelpusians. The Erinyes were deities of vangeance, and Erinys had a similar function with the goddess Dike (Justice). In the very old myth of Thelpusa Demeter-Erinys and Poseidon are divinities of the underworld in a pre-mythic period. Poseidon appears as a horse. In Greek folklore the horses had chthonic associations and it was believed that they could create springs. In European folklore the water-creatures or water-spirits appear with the shape of a horse or a bull. In Greece the river god Acheloos is represented like a bull or a man-bull. Many people when sacrificed to Demeter should make a premilinary sacrifice to Acheloos

At Phigalia Demeter had a sanctuary in a cavern and she was given the surname Melaina (black). The goddess was related to the black undeworld. In a similar myth Poseidon appears as horse and Demeter gives birth to a daughter whose name was not allowed to be told to the unitiated (At Lycosura her daughter was called Despoina). Demeter angry with Poseidon put on a black dressing and shut herself in the cavern. When the fruits of the earth were perished, Zeus sent the Moirai to Demeter who listened to them and led aside her wrath. In this cult we have traces of a very old cult of Demeter and Poseidon as deities of the underworld.

In another Arcadian myth when Rhea had given birth to Poseidon, she told Cronus that she had given birth to a horse, and gave him a foal to swallow instead of the child. In the Homeric Hymn Demeter puts a dark mourning robe around her shoulders as a sign of her sorrow. Demeter's mare-form was worshipped into historical times. The xoanon of Melaina at Phigalia shows how the local cult interpreted her, as goddess of nature. A Medusa type with a horse's head with snaky hair, holding a dove and a dolphin, probably representing her power over air and water.
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