Mercury

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Mercury is the Roman god of commerce, travel, communication, and luck — the patron of merchants, messengers, and, less reputably, thieves — whom the Romans identified with the Greek Hermes and absorbed almost wholly into his mythology. His name descends from merx, “merchandise,” and the same root that gives Latin mercari, to trade; he kept the winged sandals, the herald’s staff or caduceus, and the role of guide who escorts the dead to the underworld. A temple to him stood near the Circus Maximus from early in the republic, dedicated, the sources say, around 495 BCE, with a festival in May at which traders sprinkled their goods and themselves with water from his spring.

The blurring with Hermes was thorough and early, and it is what makes Mercury matter beyond Roman religion. Because the two had been fused, the later Greek and Egyptian habit of equating Hermes with the Egyptian Thoth carried Mercury along with it, so that the Latin West inherited the composite scribe-god of wisdom under his Roman name. Caesar, describing the gods of the Gauls, reports that they honored “Mercury” above all others as the inventor of arts and the guide of roads — his own interpretation, fitting a foreign deity to a Roman name, but a sign of how widely the figure could be cast.

That same name attached to two things that were not gods at all. The innermost planet, swift across the sky, took the name of the swift messenger; the association of the wandering star with the divine herald reached Rome through Greek astronomy, itself heir to Babylonian sky-lore. And the liquid metal the ancients called hydrargyrum — “water-silver” — became, in Latin and then across medieval Europe, mercurius: quicksilver. Alchemy made the borrowed name a doctrine. The alchemists held mercury to be one of the principles of all metals, the volatile, fluid, transformative pole answering to the fixed solidity of sulphur, and the writers gathered in collections such as The Hermetic Museum return endlessly to a “philosophical mercury” that is not quite the metal on the bench. The verbal chain ran god, planet, metal, principle — each link drawing the prestige of the one before.

A reader meeting the name in an esoteric text is rarely meeting the Roman god plainly. More often it is the planet as a marker in astrology, the metal in a recipe, or the alchemical principle that the recipe veils — and behind all of them, often, the wisdom-figure of Hermes Trismegistus, to whom the Hermetic writings were ascribed and on whose title pages “Mercurius” stood for centuries. The one name holds a god, a planet, a metal, and a sage, and the traditions that used it counted on the resemblances as more than coincidence. The historian can only note that the resemblances were assumed, traced, and built upon, long before anyone asked whether they were one thing or several.

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

→ Related: Mars · Saturn · Juno · Hermes Trismegistus