We have already seen how the rise of the grain trade brought four new deities to Rome, but there is one more chapter to our story.  The grain itself and the trade itself had now obtained their divine complements, but the sea had not yet received its due; it too must have its parallel among the gods of Rome.  And so it came to pass that again under the influence of the fateful books, though exactly when or how we cannot say, the Greek Poseidon came into Rome.  The sea had always meant much to the Greeks, and the joyful shout of Xenophon’s troops “The sea! the sea!” finds an echo all through the centuries of Greek history before and after the Anabasis.  But the multitude of islands and harbours in Greece is in marked contrast to the dearth of them in Italy, where even to-day there is no good port of call on the west coast between Naples and Civitavecchia—­and the latter would be useless, were it not for Trajan’s mole.  In Italy accordingly the sea-god Poseidon was worshipped only in the Greek colonies, where however he had two famous cults, one at Tarentum, later called Colonia Neptunia, and one at Paestum, whose old name was Poseidonia.  The Romans had worshipped deities of water in abundance, as became an agricultural people, for water meant life, and drought, death; but their deities were those of the sweet waters of springs and rivers, they knew no god of the sea.  But when the oracles brought Poseidon to Rome he was identified with an old Roman water-god Neptune, whose cult henceforward included the sea.  We do not know where the shrine of the old sweet-water Neptune had been, but his old festival had occurred on July 23.  The new Poseidon-Neptune was given a temple outside the pomerium in the Campus Martius, but the new was connected with the old in so far at least that the dedication day of the new temple was July 23, the day of the old Neptune festival.

With the introduction of Neptune, the sea-god, the state had accomplished, as it were, a sort of divine marine insurance; the transport of the grain was now watched over by a Roman god; but it was not to be expected that the cult of a sea-god would ever mean very much to the Romans.  The maritime commerce of the Eternal City was very slow in developing, and it grew to its subsequent proportions, not because the Romans of Italy engaged in it, but because those foreigners who took to the sea by nature later became Romans.  Nor did naval warfare fall to her lot until the First Punic War, and even then her victories were gained by the tactics of land fighting transferred to the decks of two ships, her own and the enemy’s, fastened together by landing-bridges, and the glory of victory was due not to Neptune but to Mars.  It was not until the civil wars at the close of the republic that real naval battles occurred, and that Neptune received his share of glory for the victory at Actium in B.C. 31, and later over Sextus Pompeius, in a temple erected by Agrippa in the Campus Martius, behind the beautiful columns of which the Roman Stock-Exchange transacts its business to-day.