Hippocampus

Poseidon did not swim. He rode, drawn across the waves by hippocampi — creatures with the forequarters of horses and the coiling tails of fish or sea serpents. Their hooves struck the surface of the water as if it were solid ground, sending up fans of spray, and their tails churned the depths behind them.

Greek and Roman artists loved the hippocampus. It appeared on coins, mosaics, temple friezes, and sarcophagi from the archaic period onward. The standard depiction showed a powerful horse body transitioning at the barrel into iridescent scales, the hindquarters replaced by a long, sinuous tail that might fork into fins or curl into a spiral. Some versions added webbed forelegs and a dorsal fin.

They pulled Poseidon's golden chariot in teams of two or four, accompanied by dolphins and Nereids. Tritons rode them individually. Sea-nymphs braided their manes with kelp. They were not monsters but divine transport — the ocean's answer to the horse.

The name combined hippos (horse) and kampos (sea monster), and it gave its name to the hippocampus of the brain — the curved structure in the temporal lobe whose shape reminded a sixteenth-century anatomist of the seahorse, which itself was named after these mythological creatures.

In Etruscan art, hippocampi carried the souls of the dead across the sea to the afterlife. The creature bridged two worlds in every sense — land and sea, life and death, the mundane horse and the impossible ocean.