Neptune (Neptunus; called by the Greeks Poseidon), in mythology, the principal god of the sea, and originally also of the rivers and springs. He was a son of Saturn and Rhea, and a brother of Jupiter, Pluto, Ceres, Vesta, and Juno. Like his brothers and sisters, he was swallowed by his father as soon as he was born, and thrown up again; or according to another account, his mother saved his life by hiding him among a flock of lambs, and offering to Saturn a young horse to which she feigned to have given birth. After Jupiter had overthrown his father, the empire of the sea fell by lot to Neptune. He is represented as being of equal dignity with his brother Jupiter, but of inferior power, though he sometimes threatened him, disputed the possession of Aegina with him, and once conspired against him. His palace was in the sea, near Euboea, and he was the especial ruler of the Mediterranean. He assisted in building the walls of Troy, and being refused the reward promised by Laomedon, ever after bore an implacable hatred to the Trojans, and in the war against Troy sided with the Greeks, often fighting on their side, causing the earth to tremble, and encouraging them with the signs of his favor. He had power over the clouds and storms, over ships and mariners, and over all other sea divinities.

He was the creator of the horse, and the teacher of horsemanship. There were many legends about him: with Jupiter he fought against Saturn and the Titans; he crushed the centaurs under a mountain in Leucosia; and he sought the hand of Thetis, but refused it through fear when Themis foretold that the son of Thetis would be greater than his father. The wife of Neptune was Amphitrite, by whom he had three children, Triton, Rhode, and Ben-thesicyme, besides a large number of other children by divine and mortal women. He was worshipped in Argolis, in the Corinthian isthmus, and in Ionia, and had a temple in Rome, in the Campus Martius. The sacrifices offered to him were bulls, bears, rams, and bridled horses, and horse and chariot races were held in his honor. He had many surnames in allusion to his various attributes. In works of art his emblems are the trident, the horse, and the dolphin; and ho is portrayed sometimes in a state of calm, sometimes m agitation, corresponding to the different aspects of the sea over which he presides.