Neptune

In Roman religion, Neptune is the deity of freshwater and the sea. He is the Greek god Poseidon's polar opposite. In Greek mythology, he is a brother of Jupiter and Pluto, who ruled over the realms of heaven, earth (including the underworld), and the oceans. Salacia is his wife's name. Neptune depictions in Roman mosaics, particularly in North Africa, were influenced by Hellenistic customs. He was most likely linked to freshwater springs before the sea. The Romans, like Poseidon, worshiped him as Neptunus equestris, the deity of horses (a patron of horse racing).

Neptune's theology is limited by his tight affiliation with the Greek god Poseidon, one of many Greek pantheon members whose theology was eventually related to a Roman deity. According to the lectisternium of 399 BC, the Greek figures of Poseidon, Artemis, and Heracles were brought and worshiped in Rome as Neptune, Diana, and Hercules. Because the Indo-Europeans lived inland and had little direct knowledge of the sea, the Romans may have reused the theology of a previous freshwater god in their worship of Neptune. Neptune is expressly named by Servius as the deity of rivers, springs, and waterways; he may be related to the Irish god Nechtan, lord of rivers and wells.

Neptune has been linked to a number of other Roman gods. He had displaced Portunus as the deity of naval victory by the first century BC; Sextus Pompeius referred to himself as the "son of Neptune." For a time, Neptune's dominion over the sea was shared with Salacia, the goddess of saltwater. Neptune was regarded as the fabled progenitor god of the Falisci (also known as Neptunia proles), standing with Mars, Janus, Saturn, and Jupiter as the deific father of a Latin tribe.