Poseidon’s earliest worshippers would not have asked him to protect their ships. In the Mycenaean period, roughly 1600 to 1100 BC, Linear B administrative tablets from centers like Pylos and Thebes show him outranking Zeus, receiving major offerings under the title wanax, a supreme overlord. He was an inland, chthonic god of earthquakes, underground water, and horses. Linguists split on his name: husband of the earth, from da and posis, or a root tied to flowing water that some link to river names like the Danube and Don. Living on limestone karst, where rivers vanish into sinkholes, the Greeks reasoned that underground water eroding the rock caused earthquakes, so the water god was the earth shaker. As populations moved to the coasts after the Bronze Age collapse, he became god of the sea.

The episode then reads his myths as biography. In Arcadia, Rhea fed Cronus a foal instead of baby Poseidon, a survival of his horse cult. After the Titanomachy, he drew the sea by lot while Zeus took the sky. His bids to be patron of cities failed: he gave Athens a saltwater spring, lost to Athena’s olive tree, and flooded the Attic plain; he lost Argos to Hera and dried up its water. His children were monsters and horses, and Plato made him the founder of Atlantis.

• On Rhodes, one tradition says he was raised in secret by the Telchines and a nymph.
• After King Laomedon of Troy refused to pay him for building the city walls, he sent a sea monster against the Trojans.
• Greeks threw live horses and bulls from cliffs into the sea as sacrifices to him.
• When Demeter took the form of a mare to escape him, he became a stallion, and she bore the immortal horse Arion.
• For Cleito on Atlantis he carved concentric rings of water and land and fathered five sets of twins, the eldest named Atlas.