Poseidon, A Compendium of the Ancient Gods

Poseidon was the god of the sea, of horses, and of earthquakes — three offices that the Greeks held to be related, the sea-god being also the god whose movement made the earth tremble, and the horse being his sacred animal because it was as swift and as untameable in its element as he was in his. He was a son of Cronus and Rhea, brother of Zeus and Hades; in the lottery after the Titanomachy he drew the sea, while Zeus drew the sky and Hades the underworld. He dwelt in a golden palace beneath the waters, drove a chariot drawn by hippocampi (sea-horses with the foreparts of horses and the tails of fish) across the surface, and carried the trident — a three-pronged spear with which he could split rocks, raise storms, and shake the earth.

His narrative roles were various. He was a frequent antagonist in the Odyssey, where his pursuit of Odysseus (in vengeance for the blinding of his son the Cyclops Polyphemus) extended the hero's wanderings to ten years. He contended with Athena for the patronage of Athens — striking the Acropolis with his trident to produce a saltwater spring, while Athena produced the olive tree, the council of the Olympians awarding the city to Athena because her gift was more useful — but he retained considerable cult on the Acropolis nonetheless, and the salt spring his trident made was visible there in classical times. He was the father, by various unions, of a great catalogue of children both heroic and monstrous: the giant Antaeus by Gaia, the giant Orion (in some traditions), the cyclopes by various unions, the winged horse Pegasus by the Gorgon Medusa, the hero Theseus by Aethra (sharing paternity with the mortal Aegeus), and many more. His loves and rapes were second only to those of his elder brother Zeus.

His great pan-Hellenic sanctuary was at the Isthmus of Corinth, where the Isthmian Games (one of the four great pan-Hellenic athletic festivals) were held in his honor every two years. His chief cult-cities were Corinth, Helike (a city in Achaea destroyed by an earthquake and tsunami in 373 BCE — a destruction that ironically struck the city most devoted to him), and the great cape sanctuary at Sounion, where the columns of his temple still stand at the southern tip of Attica.

Curator’s note

What the sources say, and what later tradition added. The sources for this bay

Homer, Iliad and Odyssey throughout (Poseidon is the principal divine antagonist of Odysseus); Hesiod, Theogony 453–457, 930; Apollodorus 1.4.6, 3.14.1 (the contest for Athens). The destruction of Helike in 373 BCE is recorded by Diodorus Siculus and others; modern marine archaeology has localized the submerged remains. The temple at Sounion, c. 440 BCE, is one of the most beautifully sited Greek temples surviving and was famously commemorated by Lord Byron's vandalism (he carved his name on a column). The horse-association of Poseidon is genuinely Indo-European-archaic and connects him to Vedic Indra and to the broader pattern of horse-and-ocean Indo-European deities.

Kin in the sources

Each tie is quoted from the entry that states it.

Child ofCronusHe was a son of Cronus and Rhea, brother of Zeus and Hades
Child ofRheaHe was a son of Cronus and Rhea, brother of Zeus and Hades
Sibling ofZeusHe was a son of Cronus and Rhea, brother of Zeus and Hades
Sibling ofHadesHe was a son of Cronus and Rhea, brother of Zeus and Hades
Rival ofOdysseushis pursuit of Odysseus (in vengeance for the blinding of his son the Cyclops Polyphemus)
Rival ofAthenaHe contended with Athena for the patronage of Athens
Consort ofGaiaHe was the father, by various unions, of a great catalogue of children both heroic and monstrous: the giant Antaeus by Gaia
Consort ofMedusathe winged horse Pegasus by the Gorgon Medusa
Parent ofPegasusthe winged horse Pegasus by the Gorgon Medusa
Parent ofTheseusthe hero Theseus by Aethra (sharing paternity with the mortal Aegeus)
SlewThe GigantesPolybotes was buried beneath the island of Nisyros, which Poseidon broke from Cos and hurled upon him
Sibling ofHeraShe was a daughter of Cronus and Rhea, sister of Zeus and Poseidon

When the sources speak

Dated witnesses for Hades and the Lesser Olympians. A date marks when the evidence was written down, not when the belief began. The whole timeline

c. 1600–1100 BCE: Mycenaean palace tablets in Linear B record offerings and divine names, but little continuous myth.
c. 1100–800 BCE: Post-palatial oral traditions and changing cult landscapes precede the surviving alphabetic epics.
late 8th–7th centuries BCE: The Iliad, Odyssey, Hesiodic Theogony and Works and Days give influential but non-exclusive divine orders.
7th–6th centuries BCE: Homeric Hymns, lyric poetry, colonization, and local sanctuary traditions multiply regional narratives.
6th–5th centuries BCE: Orphic, Pythagorean, and mystery materials develop alternative cosmogonies and afterlife doctrines.
5th century BCE: Athenian tragedy and comedy recast heroic houses and divine justice for civic audiences.
4th century BCE: Philosophers, antiquarians, and local historians interpret or criticize inherited myth.
323–31 BCE: Hellenistic poets and scholars systematize variants across an enlarged Greek world.