The hippocampus or hippocamp, also hippokampoi (plural: hippocampi or hippocamps; Greek: ἱππόκαμπος, from ἵππος, "horse" and κάμπος, "monster"), often called a sea-horse in English, is a mythological creature shared by Phoenician and Greek mythology, though the name by which it is recognised is purely Greek. It was also adopted into Etruscan mythology. The hippocampus has typically been depicted as having the upper body of a horse with the lower body of a fish.
Coins minted at Tyre around the 4th century BC show the patron god Melqart riding on a winged hippocampus and accompanied by dolphins. Coins of the same period from Byblos show a hippocampus diving under a galley.
A gold sea-horse was discovered in a horde from the kingdom of Lydia in Asia minor, dating to the 6th century BC.
In the Iliad, Homer describes Poseidon, who was god of horses (Poseidon Hippios), earthquakes, and the sea, drawn by "brazen-hoofed" horses over the sea's surface, and Apollonius of Rhodes, being consciously archaic in Argonautica, describes the horse of Poseidon emerging from the sea and galloping away across the Libyan sands. This compares to the specifically "two-hoofed" hippocampi of Gaius Valerius Flaccus in his Argonautica: "Orion when grasping his father’s reins heaves the sea with the snorting of his two-hooved horses." In Hellenistic and Roman imagery, however, Poseidon (or Roman Neptune) often drives a sea-chariot drawn by hippocampi. Thus hippocampi sport with this god in both ancient depictions and much more modern ones, such as in the waters of the 18th-century Trevi Fountain in Rome surveyed by Neptune from his niche above.