Mercury

← Encyclopedia

Mercury is the Roman god of commerce, travel, communication, and luck — patron of merchants, messengers, and, less reputably, of thieves — the divinity of everything that moves between places and changes hands. Among the gods of Rome he is the one defined least by where he sits and most by what he carries: the price agreed across a counter, the message borne from one mouth to another, the soul ferried from the world of the living to the world below. He is a god of the in-between, and the Romans, a people whose city lived by the river-traffic and the grain-ships and the contract sworn in good or bad faith, knew exactly what they were honoring when they raised his temple by the marketplace.

The name and the merchant’s god

The name itself is a ledger. Mercurius descends from merx, “merchandise,” and shares its root with mercari, to trade, and merces, wages or hire — so that to speak the god’s name is already to speak of the marketplace. (A minority etymology reaches further back, to a Proto-Indo-European root for boundary or border, which would tie him to the edge and the crossing rather than to the goods crossing it; the mercantile derivation is the one the Romans themselves heard.) His worship at Rome was, from the first, the worship of the trading classes. The god was claimed above all by the mercatores, the merchants — and pointedly so, since they were a largely plebeian body who wanted a patron and a cult of their own, set apart from the patrician-controlled priesthoods. Mercury gave them one. He was the divine guarantor of the deal, of weights and measures kept honest, of the profit sought and the wage owed.

That commercial office was inseparable from a deeper one: Mercury is the god of circulation as such — of people, goods, and words passing from hand to hand and place to place. Where Mars stood at the boundary to turn hostile force away and Juno presided over the life of the matron and the city’s women, Mercury governed the threshold as a thing to be crossed, the line as a place of exchange rather than defense. His temple’s very site spoke this function. It stood near the Circus Maximus, in the valley between the plebeian stronghold of the Aventine and the patrician Palatine — between the two Romes, on the seam where they traded — and the god who lived there was a mediator by his address as much as by his nature.

The temple and the festival of the traders

The temple of Mercury was dedicated, the annalists record, in 495 BCE, in the early, contested years of the Republic, when the plebeians and the patricians were still settling the terms on which they would share a city. Livy preserves a telling quarrel over its dedication: the honor of consecrating the new shrine was disputed between the two consuls, and the Senate, unwilling to favor either, referred the choice to the people — who passed over both consuls and gave it to a senior centurion, Marcus Laetorius, a slight to the magistrates that the sources remember as an early flexing of popular will. From the same act the collegium mercatorum, the merchants’ guild, took its formal beginning. The god and the guild were founded together.

The god’s day was the Mercuralia, the fifteenth of May. On it the merchants went out to the aqua Mercurii, Mercury’s sacred spring by the Porta Capena, the gate where the Appian Way left the city, and drew its water in vessels purified with smoke. With a sprig of laurel a trader would sprinkle the water over his goods, his ships, and his own head, and pray. The prayer that Ovid sets in the mouth of such a merchant, in the fifth book of the Fasti, his verse calendar of the Roman year, is one of the frankest pieces of religious speech the Romans left: the trader asks the god to wash away the perjuries of his past business and the false oaths of the day just gone, to keep the gods from noticing the lies he has told and will tell, and then — with no apparent sense of contradiction — to grant him good profit and the pleasure of cheating his customer. It is not piety embarrassed by commerce. It is commerce praying in its own voice, to a god who understood that the same cunning which made a good trader made a good thief, and who patronized both without preferring honesty to either. Mercury did not ask the merchant to be just. He asked only that the merchant come to him.

The herald’s gear and the guide of the dead

Mercury is known at a glance by the equipment of the road. On his feet are the talaria, the winged sandals that let him outpace every other power in the cosmos; on his head the petasus, the broad traveler’s hat, sometimes itself winged. In his hand he carries the caduceus, the herald’s staff twined with two serpents and topped with a small pair of wings — the wand of the official envoy, the sign that the one who bears it speaks under protection and must be heard. (The caduceus is the messenger’s staff and should not be confused with the single-serpent rod of Asclepius, the healer’s emblem, with which it is often muddled.) Every item is an instrument of passage: the sandals for speed, the hat for the journey, the staff for safe conduct through hostile or foreign ground.

The gravest of his offices is the last. Mercury is the psychopomp, the guide of souls — the god who leads the dead down the road to the underworld and is the one divinity free to pass that final border and return. The Romans took this from the Greek conception of the god as psychopompos, but it answered something already in their own Mercury, the god of the threshold and the unguarded crossing: death is only the last threshold, the door through which the traveler does not ordinarily come back, and the god of every other passage was the natural escort for that one too. In the underworld geography of the poets it is Mercury who musters the shades and drives them down to the river, his caduceus the same wand that elsewhere opened a city gate or stilled a quarrel. The god who guaranteed the contract and carried the message also conducted the soul; circulation, for him, ran in the end all the way out of the world.

The fusion with Hermes, and the god of the Gauls

The Romans identified Mercury with the Greek Hermes, and the identification was so early and so complete that Mercury absorbed almost the whole of the Greek god’s mythology — the cattle-theft from Apollo, the invention of the lyre, the birth from Maia on the mountain, the whole repertoire of the trickster-herald. The two gods shared too much for the match to feel like translation: both were gods of boundaries and travelers, of trade and theft, of the spoken word and the road, both wore the winged sandals and bore the herald’s staff, both led the dead. The Roman name slid over the Greek figure with almost no friction.

This habit of equation — the recognition of one’s own gods in the gods of strangers — was a reflex of the ancient Mediterranean and not merely a literary one, and Mercury became one of its most active instruments. When Julius Caesar came to describe the religion of the Gauls in the sixth book of his Commentaries on the Gallic War, he reported that of all the gods they honored Mercury most: there were images of him everywhere, he wrote, and the Gauls held him the inventor of all the arts, the guide of every road and journey, and the power with most influence over money-making and trade. Caesar was not recording a Gaulish theology in its own terms. He was fitting a foreign god to a Roman name — the practice later scholars would call interpretatio, the seeing of one pantheon through the vocabulary of another — and the native deity behind his “Mercury,” whom the epigraphic record of Gaul and Britain would later couple with local names, was a Celtic god of his own. But the choice is itself evidence: of all the names in the Roman pantheon, Mercury was the one a Roman reached for when he met a foreign god of skill, roads, and gain. The functions were portable because the god was.

The wisdom-figure under the Roman name

The most consequential of these equations ran east, into Egypt. There the Greeks under Ptolemaic rule had already identified Hermes with Thoth, the Egyptian god of writing, reckoning, and sacred knowledge, the ibis-headed scribe who recorded the verdict at the weighing of the dead — an identification grounded in their shared command of speech, intelligence, and the passage of souls. Out of that fusion, in the syncretic world of Greco-Roman Egypt, grew the figure of Hermes Trismegistus, “thrice-greatest Hermes,” the sage to whom a body of philosophical and technical revelation came to be ascribed. Because Mercury and Hermes had become a single name in Latin, the whole composite traveled west under the Roman one. Already Cicero, cataloguing the several gods who had borne the name Mercury in On the Nature of the Gods, distinguished an Egyptian Mercury credited with giving the Egyptians their laws and letters — the scribe-god in Roman dress, set down in a Latin philosophical handbook a generation before the Common Era. The Latin West would inherit the wisdom-figure not as Thoth and not even, primarily, as Hermes, but as Mercurius.

This is why the sage stands on the title pages of his own books under the Roman name. The Hermetic writings, when they reached Renaissance and early-modern readers, came labeled with formulas like Mercurius Trismegistus; the first complete English version, John Everard’s of 1650, is The Divine Pymander of Hermes Mercurius Trismegistus. The man who claimed to be that sage made the point in the flesh. On Palm Sunday of 1484 a prophet rode into Rome on a black horse, crowned with thorns, and laid on the altar of St. Peter’s a placard naming himself the angel of wisdom and Pimander — Giovanni “Mercurio” da Correggio, who wore the god’s name as the sign of the wisdom he proclaimed. His disciple, the humanist Lodovico Lazzarelli, who completed the Latin Corpus Hermeticum that Ficino had begun, addressed him in verse as Mercuri pater — Mercury, father. Two centuries on, the Flemish physician and Kabbalist Francis Mercury van Helmont carried the name as his own given name, a hermetic christening that announced what its bearer was meant to become. The god of the merchants had become, by the length of the chain Hermes had forged, the patron name of a whole tradition of revealed wisdom — and it kept his name because the wisdom had passed, like everything else of his, through the channel of exchange.

The wandering star and the living silver

Two things that were not gods at all took the name as well, and each came to it by a logic that suited the god of passage. The first was the planet. The innermost of the wandering stars, never far from the sun and quickest to return, had been the planet of Nabu to the Babylonians — their god of scribes and wisdom, the divine secretary — and the long labor of naming the sky after gods, which Greek astronomy inherited from Babylonian sky-lore, carried it westward through several hands. The Greeks first saw it as two stars, calling the morning apparition Apollo and the evening one Hermes, before their astronomers recognized the single body and settled on Hermes for it; the Romans rendered that as Mercury, the swift star for the swift god. In the astrology Rome absorbed from the Hellenistic East and codified in Ptolemy’s handbooks, the planet kept the god’s character: mutable, quick, neither hot nor cold but taking the color of whatever it stood beside, the planet of mind, language, commerce, and the in-between — the heavens’ own version of the god of the threshold.

The second was the metal. The ancients knew the strange liquid metal that ran like water and would not be held; the Greeks called it hydrargyros, “water-silver,” and Pliny, writing it up in Latin, called it argentum vivum, “living silver,” quicksilver — the only metal that moved on its own, restless, fugitive, never fixed. In medieval Latin the restless metal took the restless god’s name and became mercurius. The borrowing was apt, and then it became a doctrine. Alchemy held quicksilver to be one of the principles of all metals, the volatile, fluid, transformative pole answering to the fixed, combustible solidity of sulphur; and from the medical chemistry of Paracelsus, who set a third principle, salt, beside the two, the pair stood at the center of how matter was thought to be composed. But the alchemists were rarely speaking of the metal on the bench. The vast Latin compendia in which their tradition was gathered and printed — the Theatrum Chemicum, the Musaeum Hermeticum — return endlessly to a philosophical mercury that is the spirit and not the substance, the volatile principle veiled under the name of the liquid silver, the agent of every transformation the work sought. Robert Fludd and the writers of his century made it the very breath of the cosmos. The verbal chain had run from the god to the star to the metal to the hidden principle, each link reaching back to draw authority from the one before — and at every step it was the same trait that carried the name forward: motion that will not be fixed, the thing that crosses and changes and cannot be pinned to one place.

The textual record

The cult of Mercury at Rome is recoverable from the surviving festival calendars, from the antiquarian and poetic record, and from the modern reconstructions of the religion. The fullest scholarly synthesis is the two-volume study of Roman religion by Mary Beard, John North, and Simon Price, Religions of Rome (Cambridge University Press, 1998), with its companion sourcebook of translated texts; the standard monograph on the god himself is Bernard Combet-Farnoux, Mercure romain (École française de Rome, 1980), which traces the cult from its plebeian-mercantile origins through its imperial expansion. The ancient witnesses are largely in the public domain in their older editions. Livy’s account of the disputed dedication of 495 BCE stands in the second book of his history; Ovid’s Fasti gives the Mercuralia and the merchant’s perjury-washing prayer, available in A. S. Kline’s translation at Poetry in Translation. Julius Caesar’s report of the Gauls’ Mercury is in De Bello Gallico VI.17, hosted with the Latin and an English version at the Bill Thayer LacusCurtius archive. The migration of the name across god, planet, and metal is laid out concisely, with the source roots, at the Online Etymology Dictionary.

For the Egyptian and Hermetic afterlife of the figure under the Latin name, the controlling modern reference is Brian P. Copenhaver, Hermetica: The Greek Corpus Hermeticum and the Latin Asclepius (Cambridge University Press, 1992), whose introduction sets out how the Thoth–Hermes–Mercurius identification formed and how “Mercurius Trismegistus” came to stand on the title pages of a literature composed in Roman Egypt; Garth Fowden’s The Egyptian Hermes (Princeton University Press, 1986) reconstructs the late-antique synthesis behind it. Cicero’s enumeration of the several Mercurii, including the Egyptian one of “laws and letters,” is at De natura deorum III.56.

What persists

Strip away the star, the metal, and the sage who borrowed his name, and the figure at the root is the same in every age that handled it: a god who never stays still. He is the only power in the Roman pantheon defined by his passage rather than his place — the runner between the assembled gods and the rest of the world, the one who carries and the one who crosses. The merchants at the Porta Capena understood him precisely. They did not ask him to make them good. They asked him to keep the goods moving, the words flowing, the profit coming, and to be present at the seam where one hand lets go and another takes hold — at the counter, on the road, at the gate, and at the last gate of all, where he alone among the gods could lead a soul across and find his own way back. That is the god the traders sprinkled with the water of his spring: not the keeper of any one thing, but the patron of the passing of all things from hand to hand.

→ In the library: The Divine Pymander of Hermes Mercurius Trismegistus (Everard, 1650) · Waite — The Hermetic Museum (1893)

→ Related: Mars · Saturn · Juno · Hermes · Hermes Trismegistus · Serapis · Artemis · Ancient Roman Religion · Astrology · Alchemy · Paracelsus · Robert Fludd · Corpus Hermeticum · Lodovico Lazzarelli · Francis Mercury Van Helmont