The Roman nature of Neptune

Some scholars argue that Indo-European people, having no direct knowledge of the sea as they originated from inland areas, reused the theology of a deity originally either chthonic or wielding power over inland freshwaters for the god of the sea as contact was made with seafaring peoples. They then paired him with Salacia, the goddess of saltwater who subsequently came to represent the virile force of Neptune.  This conclusion was arrived at by the numerous findings of inscriptions mentioning Neptune in the proximity of such locations. Servius the grammarian also explicitly identified Neptune as the deity in charge of all the rivers, springs, and waters.

Before the 1st century BCE, the Romans thanked the god Portunus or Fortunus for naval victories, but Neptune supplanted him in this role by at least the first century BCE when Sextus Pompeius, younger son of Pompey Magnus, called himself "son of Neptune." 

Like Poseidon, Neptune was also worshipped by the Romans as a god of horses, under the name Neptunus Equester, a patron of horse-racing.  This may account for the marine-themed sculptures, such as dolphins, in the circus that were used to mark laps during each race. In Roman mythology, Neptune worked with Minerva to create the chariot.

Neptune was also considered the legendary progenitor god of a Latin stock, the Faliscans, who called themselves Neptunia proles. In this respect he was the equivalent of Mars, Janus, Saturn and even Jupiter among Latin tribes. 

The Neptunalia was the festival of Neptune celebrated by the Romans on July 23, at the height of summer. The festival included free and unrestrained merrymaking, and outings in the wood between the Tiber and the Via Salaria where springwater and wine were drunk to escape the heat. Neptune is one of only four Roman gods to whom it was appropriate to sacrifice bulls, the other three being Apollo, Mars and Jupiter, although Vulcan was also allowed the offering of a red bull and a red bull calf which symbolized the force of his forge.

Neptune is often depicted with two paredrae (accompanying deities), Salacia and Venilia, who represent the overpowering and the tranquil aspects of water. Salacia would impersonate the gushing, overbearing waters and Venilia the still or quietly flowing waters.

Neptune, the god of the sea, stands completely nude with his weight on his right leg. Originally, his raised right hand would have supported a trident, and he may have held a dolphin or ship's ornament in his left. Even with these attributes missing, the figure's unkempt hair, spiky crown of water plants, and mobile, restless-looking pose identify him as the sea god.

The elongated but muscular physique, small head, and majestic stance, as well as the way in which the figure’s arms extend into the space around it, derive from the innovations of the Greek sculptor Lysippos in the late 300s B.C.E. The mannered and almost playful exaggeration of the traits in this statuette, however, typifies a Roman revival of the style in the late 100s B.C.E. Image courtesy of the J. Paul Getty Museum.

Neptune in the caves of the gardens of the Château de Vaux-le-Vicomte in Maincy, France courtesy of Wikimedia Commons contributor Velvet.

Fountain of Neptune by Antonio Della Bitta (1878) that I photographed in the Piazza Navona in Rome, Italy.