e was outside the _pomerium_ on
the Aventine side of the Circus Maximus. It was in this temple of the
merchant god that the primitive Chamber of Commerce (_collegium
mercatorum_) had its beginning, an association, partly sacral, partly
commercial, whose members, the _mercuriales_, are frequently met with
in literature and also in inscriptions, one of which has been found as
far away as the island of Delos. In the actual cult of the Romans
Mercury never regained the many-sidedness which he had lost in coming to
them merely as a god of trade. In this capacity he appears on the
sextans of the old copper coinage, and under the empire he went into the
provinces as the companion of Mars, since the merchant went side by side
with the soldier. On the contrary when in the third century before
Christ Greek literature came to Rome, this simple idea of Mercury was
reinforced by many new Greek ideas and he entered into Roman poetry with
all the attributes and functions of Hermes; but this had little or no
effect on the cult and there were no great rivals to the old temple near
the Circus Maximus, no cult-centre with advanced Greek ideas, as we have
seen spring up in the case of Hercules, Castor, Minerva, and Diana.

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, f