Poseidon was a son of Cronus and Rhea. In most accounts he is swallowed by Cronus at birth but later saved, with his other brothers and sisters, by Zeus. However in some versions of the story, he, like his brother Zeus, did not share the fate of his other brother and sisters who were eaten by Cronus. He was saved by his mother Rhea, who concealed him among a flock of lambs and pretended to have given birth to a colt, which she gave to Cronus to devour. According to John Tzetzes the kourotrophos, or nurse of Poseidon was Arne, who denied knowing where he was, when Cronus came searching; according to Diodorus Siculus Poseidon was raised by the Telchines on Rhodes, just as Zeus was raised by the Korybantes on Crete.
According to a single reference in the Iliad, when the world was divided by lot in three, Zeus received the sky, Hades the underworld and Poseidon the sea. In the Odyssey (v.398), Poseidon has a home in Aegae.
The foundation of Athens
Athena became the patron goddess of the city of Athens after a competition with Poseidon. Yet Poseidon remained a numinous presence on the Acropolis in the form of his surrogate, Erechtheus. At the dissolution festival at the end of the year in the Athenian calendar, the Skira, the priests of Athena and the priest of Poseidon would process under canopies to Eleusis. They agreed that each would give the Athenians one gift and the Athenians would choose whichever gift they preferred. Poseidon struck the ground with his trident and a spring sprang up; the water was salty and not very useful, whereas Athena offered them an olive tree. The Athenians (or their king, Cecrops) accepted the olive tree and along with it Athena as their patron, for the olive tree brought wood, oil and food. After the fight, infuriated at his loss, Poseidon sent a monstrous flood to the Attic Plain, to punish the Athenians for not choosing him. The depression made by Poseidon’s trident and filled with salt water was surrounded by the northern hall of the Erechtheum, remaining open to the air. “In cult, Poseidon was identified with Erechtheus,” Walter Burkert noted; “the myth turns this into a temporal-causal sequence: in his anger at losing, Poseidon led his son Eumolpus against Athens and killed Erectheus.”
The contest of Athena and Poseidon was the subject of the reliefs on the western pediment of the Parthenon, the first sight that greeted the arriving visitor.
This myth is construed by Robert Graves and others as reflecting a clash between the inhabitants during Mycenaean times and newer immigrants. It is interesting to note that Athens at its height was a significant sea power, at one point defeating the Persian fleet at Salamis Island in a sea battle.