the chief marine divinity of the Romans. His name is probably connected with the verb ναίω or nato, and a contraction of navitunus. As the early Romans were not a maritime people, and had not much to do with the sea, the marine divinities are not often mentioned, and we scarcely know with any certainty what day in the year was set apart as the festival of Neptunus, though it seems to have been the 23rd of July (X. Kal. Sext.). His temple stood in the Campus Martins, not far from the septa; but respecting the ceremonies of his festival we know nothing, except that the people formed tents (umbrae) of the branches of trees, in which they probably rejoiced in feasting and drinking (Varro, de Ling. Lat. 6.19; Hor. Carm. 3.28; Paul. Diac. p. 377, ed. Müller; Tertull. de Spect. 6; P. Vict. Reg. Urb. IX.; Dict. of Ant. s. v. Neptunalia). When a Roman commander sailed out with a fleet, he first offered up a sacrifice to Neptunus, which was thrown into the sea (Cic. de Nat. Deor. 3.20; Liv. 29.27). In the Roman poets Neptunus is completely identified with the Greek Poseidon, and accordingly all the attributes of the latter are transferred by them to the former. [POSEIDON.]