The hippocampus (Greek: ἱπππόκαμπος, joining ἵππος, horse, plus κάμππος kampos, monster) is a mythological creature shared by Phoenician and Greek mythology. It has typically been described as horse on the front part of its body and fish on the back part with a scaly tail, like a seahorse.
Coins minted in Tyre around the 4th century BCE show Melcarte, the city's tutelary god, on a winged hippocampus and accompanied by dolphins. Silver coins of the same period from Biblos display a hippocampus diving under a galley with three hoplites on its obverse.
In Greek mythology, the hippocampus served as a companion and mount for the nereids and as a draft animal for Poseidon's chariot. Beings with similar characteristics appear in the art of other cultures, including Mesopotamia and India. It was also depicted in bronzes, silverware and paintings from Roman antiquity to the Baroque period.
Created by Poseidon from sea foam, they are animals with bright, rainbow-like fish tails, and the front of their bodies are white steed. Hippocampi are the mounts of Poseidon's army.
Homer associates Poseidon, who was the god of horses, with tremors on land and sea, caused by the horses' bronze hooves on the surface of the sea, and Apollonius of Rhodes, being consciously archaic in Argonautica, describes Poseidon's horse emerging from the sea and galloping away across the Libyan sands.
In Hellenistic and Roman images, however, Poseidon (or Neptune) often carries a sea chariot pulled by hippocampi. Thus, hippocampi are associated with this god in both ancient and more modern depictions, such as in the 18th century waters at the Trevi Fountain in Rome.
The appearance of hippocampi in freshwater and saltwater is counterintuitive to a modern audience, though not the ancient one. The Greek image of the natural hydrological cycle does not take into account the condensation of water in the atmosphere in the form of rain to replenish the water table, but imagined seawater being "replenished" through caves and aquifers.
The taxonomic genus Hippocampus, of the seahorses, has its name derived from the hippocampus, as well as the organ hippocampus, the main seat of memory and an important component of the human limbic system, which was so named by Giulio Cesare Aranzio in 1587 because of its resemblance to a seahorse.
As an integral part of Greek mythology, the hippocampus appears in several works of popular culture, such as Saint Seya.