The caduceus, depicted as a staff entwined by two snakes and often topped with wings, is the traditional symbol of the Greek god Hermes. Hermes was the god of trade, deception, thievery, eloquence, negotiation, and alchemy, with no traditional association with healing or medicine.
Medicine's traditional symbol, by contrast, is the Rod of Asclepius, a plain staff wound by a single serpent and named for Asclepius, the Greek god of medicine and healing. Predominantly in the United States, however, the caduceus became associated with medicine in the late 19th and early 20th centuries, a result of misunderstandings of classical iconography.
Early use in a possible medical context
Before the ancient Romans and Greeks (about 2612 BCE), older representations from Syria and India of sticks and animals looking like serpents or worms are interpreted by some as a direct representation of traditional treatment of dracunculiasis, the Guinea worm disease.Dickson Despommier, People, Parasites, and Plowshares: Learning from Our Body's Most Terrifying Invaders, Columbia University Press, 2016 (first edition in 2013), pages 147-163 (chapter 7 on Dracunculus medinensis), .
While there is ample historical evidence of the use of the Caduceus, or Herald's Staff, to represent Hermes or Mercury (and by extension commerce and negotiation), early evidence of any symbolic association between the Caduceus and medicine or medical practice is scarce and ambiguous. It is likely linked to the alchemical "universal solvent", Azoth, the symbol of which was the caduceus.
The Guildhall Museum in London holds a 3rd-century oculist's seal with Caduceus symbols both top and bottom. The seal was apparently used to mark preparations of eye medicine. It is believed likely that rather than being evidence of a medical association per se, this is rather an allusion to the words of the Greek poet Homer who described the Caduceus as "possessing the ability to charm the eyes of men", which relates to the business of an oculist.
Walter Friedlander proposed that early association of the Caduceus with medicine might have derived from the association of Hermes Trismegistus ("Thrice-Great Hermes") with early chemistry and medicine as aspects of alchemy as an esoteric practice. He notes that "there are very definite connections between medicine and (Hermes)-Thoth, who later became known as Hermes Trismegistus.Friedlander 1992, p. 41. [...] although these various factors may link Hermes/Mercury, along with his Caduceus, with alchemical medicine, they may just as well link all the other non-medical aspects of alchemy with Hermes/Mercury and the Caduceus".Friedlander 1992, p. 76.
Despite a long tradition of (the tendency of the ancient Greeks to identify foreign deities with their own gods), determination of the equivalence of deities is a complex matter. The role of Hermes in the afterlife was limited to guiding souls of the deceased, whereas the powerful Egyptian god Thoth was truly lord of the underworld and master of death. Together with Osiris, he presided over the panel of forty-two divine judges that assessed the souls of the deceased for reward or punishment in the afterlife. Thoth was at times depicted with two staves encircled by one cobra each, which might well have influenced the iconography of Hermes' caduceus. However, in ancient Egypt the snake staff represented the attribute of a powerful sorcerer, not a merchant or messenger. Compared to Hermes, Thoth was associated much more with magic and with potent actions preserving balance in the divine world, than with the unpredictable whims of a trickster deity.
Depictions similar to the caduceus also occurred in bronze age Mesopotamia as devotional emblems for various major or minor deities, or as snakes embodying the deity itself. Ancient examples of attributes similar to the caduceus, or to aspects of Hermes' portfolio of divine roles, include the Sumerian messenger and snake god Nirah, the occasional depictions of the major goddess Innana holding a scepter with two winding snakes (which lacked the wings of a caduceus), and the benevolent Egyptian goddess Wadjet who was often depicted as a winged cobra.
If the caduceus was inspired by and adapted from an amalgam of serpent depictions in other cultures, probably with changes in explanatory myths and divine prerogatives, then Greek mythology might well have created an exaggerated impression that the origins of the caduceus were entirely separate from those of the rod of asclepius. From the perspectives of ethnography and literary history, their cultural and iconographic origins were probably deeply entwined as part of the complex and artistically fluid history of snakes as deities or as divine symbols for healing, magic and protective rituals.
Medieval times
The Caduceus became a symbol of alchemy and pharmacy in medieval Europe. Its first appearance as a medical symbol can be traced back to 1st−4th century CE in oculists' stamps that were found mostly in Celtic areas, such as Gaul, Germany and Britain, which had an engraving of the name of the physician, the name of the special medicine or medical formula and the disease for which the medicine was to be used.
Medieval alchemy used the Caduceus to represent preparations containing quicksilver, later known as mercury. Quicksilver (named ) was believed to be the basis of all substances and this element has been represented by the caduceus for many centuries.
Based on the medieval European use of the caduceus to signify pharmacy, Bavarian printer Erhard Ratdolt used the caduceus in his medical manuscripts from 1486 CE. Others followed (not uncontroversially, see section Modern times below). Sir William Butts, physician to Henry VIII, was the first physician to adopt it as his emblem. The rod of Asclepius, since the 5th century CE, resurfaced in 1544 CE. A publication of the medical writings of Avicenna, a Persian physician, had it at the frontispiece.
Modern times
Beginning with the 16th century there is limited evidence of the use of the caduceus in what is arguably a medical context. However, this evidence is also ambiguous. In some cases it is clear that the caduceus symbolized wisdom, without any specific medical connotations.
The caduceus appears in a general medical context in the printer's device used by the Swiss medical printer Johann Frobenius (1460–1527), who depicted the staff entwined with serpents and surmounted by a dove, with a biblical epigraph in Greek, "Be ye therefore wise as serpents and harmless as doves" (Matthew 10:16, here in the KJV translation), in keeping with the connotations of the caduceus as a symbol of messengers and publishers based on the association of Hermes or Mercury with eloquence and negotiation. Friedlander observed that Frobenius could hardly be considered a medical printer, as had previously been asserted, noting that in a review of 257 of the works bearing this printer's device only one was related to medicine. Similar use of the caduceus in printers' marks continues to the present day, with companies including F. A. Davis Company still using the symbol as an element of their insignia.
There are a few other examples of use in this period. It may have been used as a symbol by Sir William Butts, physician to Henry VIII. Similarly, physician John Caius, founder of Caius College, Cambridge, and at the time President of the Royal College of Physicians, during official visits to his eponymous college, had carried before him a silver caduceus on a cushion, and later presented this artefact to the college, where it remains in the college's possession. This use was adduced by the medical historian (and primary apologist for the use of the caduceus in a medical context) Fielding Garrison to support his argument that the caduceus was used as a symbol of medicine as far back as the 16th century. However, as Walter Friedlander noted, "what Caius used was a non-specific herald's wand, rather than the caduceus of Hermes." In support of this assertion he quotes Caius's own words on why he chose a herald's wand as a symbol, making it clear that he chose it as a symbol of prudence. This same passage was also earlier referenced by Engle in refuting Garrison's claim. Engle and Friedlander are not the only ones to have noted that the use of the Caduceus by Caius had nothing to do with supposed medical symbolism; as indicated in a publication produced by the Royal College of Physicians itself: "[...] by introducing the caduceus into the ceremony of the College of Physicians, Caius unintentionally added to the confusion between the two emblems for later times, when few people understand the visual signs with which he was so familiar."
In support of the idea that the caduceus had a long-standing association with medicine, Garrison also mentioned the fact that the English medical printer Churchill used the symbol as a printer's device, beginning some time around 1844. Friedlander has examined this subject in detail, and shows that Churchill was well aware that the rod of Asclepius was the accepted symbol of medicine. He is, it seems, inclined to think that the adoption of the caduceus in this context probably had something to do with the relation between publishing and the role of Mercury as a messenger and scribe. He notes, however
In any case, in Great Britain, as late as 1854, the distinction between the rod of Asclepius and the caduceus as symbols of two very different professions was apparently still quite clear. In his article On Tradesmen's Signs of London A.H. Burkitt notes that among the very old symbols still used in London at that time, which were based on associations between pagan gods and professions, "we find Mercury, or his caduceus, appropriate in trade, as indicating expedition. Esculapius, his Serpent and staff, or his cock, for professors of the healing art".
Adoption by the US military
Widespread confusion regarding the supposed medical significance apparently arose as a result of events in the United States that occurred in the second half of the 19th century. As pointed out by Garrison, the caduceus had appeared on the chevrons of Army hospital stewards as early as 1856 (William K. Emerson indicates the insignia was adopted earlier, in 1851). It has been asserted that this was a result of ignorance or misinterpretation regarding the pre-existing designation of the rod of Asclepius by the Surgeon General of the United States for this purpose. Hospital stewards were not physicians; they played a supporting role preparing drugs for surgeons, supervising nurses and cooks, maintaining accounting and medical records, and in emergencies sometimes performed minor surgery or provided prescriptions.George Winston Smith, Medicines For The Union Army: The United States Army Laboratories During The Civil War, Haworth Press, 2001, pp. 14–15.
Later, in 1871, the Surgeon General designated the caduceus as the seal of the Marine Hospital Service (destined to become the U.S. Public Health Service in 1912). Gershen states that the change was for aesthetic reasons,Barton J. Gershen, Word Rounds: A history of words, both medical and nonmedical, and their relationship to one another, Flower Valley Press, 2001, p. 45. whereas Friedlander states the caduceus was adopted by the Marine Hospital Service "because of its relationship with merchant seamen and the maritime industry".