Before ruling the sea, Poseidon outranked Zeus on Mycenaean clay tablets
Most people know Poseidon as the trident-wielding sea god. Bronze Age scribes saw him differently: on Linear B tablets his name turns up more often than that of Zeus, he was chief deity at Pylos and Thebes, and his oldest title was earth-shaker, a god of quakes and horses long before waves.
Classical Greeks counted Poseidon among the twelve Olympians, lord of the sea, storms, earthquakes and horses, and a guardian of sailors and of many cities and colonies. Homer explains his realm through a lottery: after Cronus was overthrown, his three sons divided the world, with Zeus drawing the sky, Hades the underworld and Poseidon the sea, while Earth and Olympus stayed shared. Romans knew him as Neptune.
The horse link runs deep. A blow of his trident was said to open springs, and in Greek the words for horse and spring are related. In remote Arcadia he was worshipped as a horse himself under the name Hippios. One Arcadian myth has Demeter turn into a mare to escape him; he became a stallion, and she bore a swift horse named Arion plus a daughter whose name was kept secret from the uninitiated.
His name is a puzzle. One theory splits it into lord and a Doric word for earth, making him husband of the earth, but Walter Burkert calls that reading impossible to prove, and Robert Beekes sees no evidence the syllable meant earth. Another reading links it to a root for water, as in the rivers Danube and Don, giving master of waters. Beekes himself leans towards a Pre-Greek origin. Plato, in the Cratylus, offered playful guesses such as a god who knew many things.
Myths keep casting him as a sore loser. He lost the contest for Athens to Athena and flooded the Attic plain in revenge, though he kept a foothold on the Acropolis through Erechtheus. In the Iliad he backs the Greeks against Troy, yet in the Odyssey, after Odysseus blinds his son, the Cyclops Polyphemus, his storms wreck the hero's ship and stretch the voyage home by ten years.
Source: Poseidon
