Poseidon, in ancient Greek religion, god of the sea (and of water generally), earthquakes, and horses. He is distinguished from Pontus, the personification of the sea and the oldest Greek divinity of the waters. The name Poseidon means either “husband of the earth” or “lord of the earth.” Traditionally, he was a son of Cronus (the youngest of the 12 Titans) and of Cronus’s sister and consort Rhea, a fertility goddess. Poseidon was a brother of Zeus, the sky god and chief deity of ancient Greece, and of Hades, god of the underworld. When the three brothers deposed their father, the kingdom of the sea fell by lot to Poseidon. His weapon and main symbol was the trident, perhaps once a fish spear. According to the Greek poet Hesiod, Poseidon’s trident, like Zeus’s thunderbolt and Hades’ helmet, was fashioned by the three Cyclopes.
As the god of earthquakes, Poseidon was also connected to dry land, and many of his oldest places of worship in Greece were inland, though these were sometimes centred on pools and streams or otherwise associated with water. In this aspect, he was known as enosichthon and ennosigaios (“earth-shaker”) and was worshipped as asphalios (“stabilizer”). As the god of horses, Poseidon is thought likely to have been introduced to Greece by the earliest Hellenes, who also introduced the first horses to the country about the 2nd century BCE. Poseidon himself fathered many horses, best known of which was the winged horse Pegasus by the Gorgon Medusa.