Neptunus was god of irrigation, Italic and Roman. The deity was identified with planet Neptune but his origin is thought to have come from a god of agriculture concerned with watering. His celebration occurred at the festival of Neptunalia on July 23. Also, he was the patron of horse racing. Later he became syncretized with Poseidon, but Neptune’s modern association with the sea is a misrepresentation. A.G.H.
Jordan, Michael, Encyclopedia of Gods, New York, Facts On File, Inc. 1993, p. 181