I.Neptune from "Roman Antiquities, and Ancient Mythology" by Charles K. Dillaway
II.Neptune from "Myths and Legends of Ancient Greece and Rome" by E.M. Berens
Neptune was the son of Saturn, and Rhea or Ops, and brother of Jupiter. When arrived at maturity, he assisted his brother Jupiter in his expeditions, for which that god, on attaining to supreme power, assigned him the sea and the islands for his empire. Whatever attachment Neptune might have had to his brother at one period, he was at another expelled heaven for entering into a conspiracy against him, in conjunction with several other deities; whence he fled, with Apollo, to Laomedon, king of Troy, where Neptune having assisted in raising the walls of the city, and being dismissed unrewarded, in revenge, sent a sea-monster to lay waste the country.
On another occasion, this deity had a contest with Vulcan and Minerva, in regard to their skill. The goddess, as a proof of her's, made a horse, Vulcan a man, and Neptune a bull, whence that animal was used in the sacrifices to him, though it is probable that, as the victim was to be black, the design was to point out the raging quality and fury of the sea, over which he presided. The Greeks make Neptune to have been the creator of the horse, which he produced from out of the earth with a blow of his trident, when disputing with Minerva who should give the name to Cecropia, which was afterwards called Athens, from the name in Greek of Minerva, who made an olive tree spring up suddenly, and thus obtained the victory.
In this fable, however, it is evident that the horse could signify nothing but a ship; for the two things in which that region excelled being ships and olive-trees, it was thought politic by this means to bring the citizens over from too great a fondness for sea affairs, to the cultivation of their country, by showing that Pallas was preferable to Neptune, or, in other words, husbandry to sailing, which, without some further meaning, the production of a horse could never have done. It notwithstanding appears that Neptune had brought the management of the horse, as likewise the art of building ships, to very great perfection; insomuch that Pamphus, who was the most ancient writer of hymns to the gods, calls him the benefactor of mankind, in bestowing upon them horses and ships which had stems and decks that resembled towers.
If Neptune created the horse, he was likewise the inventor of chariot-races; hence Mithridātes, king of Pontus, threw chariots, drawn by four horses, into the sea, in honor of Neptune: and the Romans instituted horse-races in the circus during his festival, at which time all horses ceased from working, and the mules were adorned with wreaths of flowers.
Neptune, represented as a god of the sea, makes a considerable figure: he is described with black or dark hair, his garment of an azure or sea-green color, seated in a large shell drawn by whales, or sea-horses, with his trident in his hand, attended by the sea-gods Palæmon, Glaucus, and Phorcys; the sea-goddesses Thetis, Melita, and Panopēa, and a long train of Tritons and sea-nymphs.
The inferior artists represent him sometimes with an angry and disturbed air; and we may observe the same difference in this particular between the great and inferior poets as there is between the bad and the good artists. Thus Ovid describes Neptune with a sullen look, whereas Virgil expressly tells us that he has a mild face, even where he is representing him in a passion. Even at the time that he is provoked, and might be expected to have appeared disturbed, and in a passion, there is serenity and majesty in his face.
On some medals he treads on the beak of a ship, to show that he presided over the seas, or more particularly over the Mediterranean sea, which was the great, and almost the only scene for navigation among the old Greeks and Romans. He is standing, as he generally was represented; he most commonly, too, has his trident in his right hand: this was his peculiar sceptre, and seems to have been used by him chiefly to rouse up the waters; for we find sometimes that he lays it aside when he is to appease them, but he resumes it when there is occasion for violence. Virgil makes him shake Troy from its foundation with it; and in Ovid it is with the stroke of this that the waters of the earth are let loose for the general deluge. The poets have generally delighted in describing this god as passing over the calm surface of the waters, in his chariot drawn by sea-horses. The fine original description of this is in Homer, from whom Virgil and Statius have copied it.
In searching for the mythological sense of the fable, we must again have recourse to Egypt, that kingdom which, above all others, has furnished the most ample harvest for the reaper of mysteries. The Egyptians, to denote navigation, and the return of the Phœnician fleet, which annually visited their coast, used the figure of an Osīris borne on a winged horse, and holding a three-forked spear, or harpoon. To this image they gave the name of Poseidon, or Neptune, which, as the Greeks and Romans afterwards adopted, sufficiently proves this deity had his birth here. Thus the maritime Osīris of the Egyptians became a new deity with those who knew not the meaning of the symbol.
The Romans worshipped Poseidon under the name of Neptune, and invested him with all the attributes which belong to the Greek divinity.
The Roman commanders never undertook any naval expedition without propitiating Neptune by a sacrifice.
His temple at Rome was in the Campus Martius, and the festivals commemorated in his honour were called Neptunalia.