Neptune is the god of the sea, a brother of Jupiter and Pluto. He is analogous but not identical to the god Poseidon. The Roman conception of Neptune owed a great deal to the Etruscan god Nethuns. Originally he was an Italic god paired with Salacia, possibly the goddess of the salt water. At an early date (399 BC) he was identified with Poseidon, when the Sibylline books ordered
|First||Controls any sea animal|
|Second||Controls sea whether|
In earlier times it was the god Portunes or Fortunus who was thanked for naval victories, but Neptune supplanted him in this role by at least the first century BC, when Sextus Pompeius called himself "son of Neptune".
Neptune was associated as well with fresh water, as opposed to Oceanus, god of the world-ocean.
Like Poseidon, Neptune was also worshipped by the Romans as a god of horses, under the name Neptune Equester, patron of horse-racing.
Neptune was also considered the legendary progenitor god of a Latin stock, the Faliscans - ancient Italian people - who called themselves Neptunia proles. In this respect he was the equivalent of Mars, Janus, Saturn and even Jupiter among Latin tribes.