The chronicle of the year B.C. 495 tells us that there was a dispute in that year as to who should dedicate the temple of Mercury.  This is Mercury’s first appearance in our sources.  The circumstances of the vowing of the temple have been omitted through some oversight, but in spite of this the connexion of his introduction with the Sibylline books is beyond all reasonable doubt, for the simple reason that the guardians of the oracles always looked after his cult in all subsequent time.  Notwithstanding the suddenness of his appearance and the silence of the chronicle, his story is quite clear and his past history easy to restore, at least in outline.

The versatile Hermes, who as messenger of the gods plays a part in so many Greek myths, became in the course of time among other things associated with travelling, as god of roads, and also with trade, partly because trading necessitates travelling, and partly because Hermes was also the protector of the market-place in which the trading was done.  Thus he was called “Hermes Protector of the Merchant” (Empolaios) and in this capacity went into the colonies of Greece, including those of Southern Italy.  Thus Hermes travelled with the grain merchant from Cumae and became known to the Romans.  They however knew him merely as the god of trade, and their name for him is nothing but the translation into Latin of his Greek cult-title:  Empolaios = Mercurius.  For a long time it was thought that there had existed a Mercurius among the original gods of Rome, but the traces of this old god are apparent rather than real and suggest one phase of that pastime of which the later Romans were so fond, that of writing history backwards and putting an artificial halo of antiquity about the gods whom they borrowed from Greece.  Thus Mercury was received into the state-cult at about the time when the grain trade began, and was, as it were, the divine representative of the interest which the Roman state took in the whole transaction.  His temple 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.