MERCURIO. — An ancient Roman deity, who appears in the earliest lists of the twelve gods. The name itself, Mercurius (from merx, mercari), clearly accounts for the god’s original character—as protector of commerce—whose cult received impetus not only from Rome’s relations with Cumae and Sicily, but above all when the Ἔρμης ἐμπόλαος, that is, Hermes (v.) protector of merchants, entered Rome; from him he also adopted his other attributes.
M. was venerated especially by merchants, who celebrated his feast on 15 May (feriae Iovi Mercurio Maiae), the anniversary of the dedication of his temple, erected in 495 B.C. near the Circus Maximus. In the same year as the dedication, according to tradition (Livy, V, 13, 6), the public grain supply was organized and a special corporation (collegia, which later spread widely throughout Italy and beyond) of merchants was established. These merchants, called sometimes mercatores, sometimes mercuriales, had their headquarters in the pomorium. On the Ides of May, they used to sprinkle themselves with laurel branches soaked in the fons Mercurii, near the Porta Capena (not far from the temple), praying to the god to “wash” them of the lies they had told in the adjacent forums in the exercise of their trade (Ovid, Fasti, V, 670 ff.). The effigy of M. is found for the first time on the aes grave of the mid-fourth century B.C.; here too it is an evident imitation of the Greek Hermes: a youthful, beardless face and a petasus equipped with two small wings.
Altheim, on the other hand, maintains that the name Mercurius was originally the name of a gens Mercuria, of which Hermes was the gentilician god in Etruria, and that consequently both M. and the Greek god were later introduced into Rome by the Etruscans themselves.
Cesare D'Onofrio