In the Middle Ages and into the Renaissance, Europeans knew that unicorns were real. After all, their horns were the treasured possessions of royalty, nobility, and even clergy. Charles VI of France had one, as did Lorenzo de Medici, and Danish rulers sat on a throne carved out of them. Queen Elizabeth I had a fully intact horn she used as a scepter; it was valued at 10,000 pounds—roughly the cost of a castle in her day. In fact, unicorn horns were considered so valuable the Elizabethan dramatist John Dekker wrote that one was "worth a city."
But unicorns horns weren't prized just for their beauty or rarity, or as tokens of extreme wealth. They were believed to be powerful defense against disease—and poison.
From the beginning, accounts of the unicorn emphasized their healing and purifying properties. Ctesias wrote, "Those who drink out of these horns, made into drinking vessels, are not subject, they say, to convulsions or to the holy disease [epilepsy]. Indeed, they are immune even to poisons if, either before or after swallowing such, they drink wine, water, or anything else from these beakers." Similar accounts appeared for centuries: Around the 3rd century CE, the Greek intellectual Philostratus wrote that "the Indians make drinking-cups from this horn, which have such virtue that the man who drinks from one will for one whole day neither fall ill, nor feel pain if wounded, nor be burned by passing through fire, nor even be affected by poisons which he could not swallow at any other time without harm."
By the 12th century, a German nun known for her saintly visions, Hildegard of Bingen, recommended a paste of powdered unicorn liver and egg yolk as a cure for leprosy, although she conveniently noted that it could fail if the "leper in question happens to be one whom death is determined to have or else one whom God does not wish to be cured." Unicorn hide was also recommended in boots and belts, partly as prevention for that greatest scourge of the Middle Ages: plague.
Belief in the healing powers of the unicorn focused especially on its mysterious, twisting horn. The substance, often called alicorn, was associated with great purity as well as healing, sometimes with religious overtones (the purity of the white animal was thought to be connected to Jesus Christ, and the horn to his cross). Hunters in search of a unicorn were supposed to lure the animal with a female virgin, capturing the animal once it fell asleep in her lap.
Of course, no such hunters were ever successful. Objects portrayed as being made from unicorn sometimes came from rhinoceroses or mammoth fossils but most often in Europe from narwhals, which were hunted by the Vikings in the North Atlantic. The Vikings harvested the narwhals' spiraling tusks and sold them on to traders who either didn't know, or didn't care, about their true origins in the sea.
Once obtained, alicorn could be taken in many forms. Powdered, it was applied to dog bites and other wounds or consumed as treatment for plague, gout, and other diseases. The influential German physician Johann Schröder recommended it for childhood epilepsy. And although other physicians numbered among the earliest skeptics, apothecaries used unicorns widely in their potions. Eau de licorn—water purified by the introduction of unicorn's horn or by being poured through a hollowed-out segment of horn—was also widely sold and reputed to have health benefits.
While the extraordinary cost of the intact horns made them showpieces for the rich, powdered unicorn horn was an affordable remedy for the average citizen. This was largely because other substances could be easily substituted: horse hoofs, fossils, and other types of horn. In fact, the widespread problem of fraud led to frequent tests of the authenticity of the horn itself, including presenting it to spiders and scorpions and observing to see if they avoided it or died. If they did, the item was thought to be genuine horn.
Poisoning was particularly feared during the Middle Ages and into the Renaissance by the back-stabbing royalty and nobility keen to maintain their positions, not to mention their lives. Such an insidious crime required extraordinary measures: While European royalty kept other poison-detectors, including rubies, bezoar stones, and griffin claws, unicorn horn was a favored material for protection as well.
Whole unicorn horns were deployed on dining tables as poison detectors, while fragments of horn, called touches by the French, could be touched or dipped to plates of food to detect the presence of toxins. They could also be hung on chains or mounts of precious metal (actually less valuable materials, pound for pound, than the horn itself). French royalty had utensils made with alicorn, while other members of the European nobility had the horn inset into jewelry. The horn was expected to provide an alert to the presence of poison by changing color, sweating beads of moisture, or actually steaming. Alicorn might also be dipped into water or run over the actual linens and wall hangings in a banquet hall. Goblets fashioned from unicorn horn were also made across the continent; some believed these would shatter upon contact with a contaminated beverage.
While some medical writers, such as the famed French surgeon Ambroise Paré, were skeptical of the powers of the unicorn horn, many others believed in its merits. The Italian scholar and naturalist Andrea Bacci wrote a defense of the horn's use in 1573, telling the story of a man who consumed a poisoned cherry but was saved thanks to unicorn horn dissolved in wine. He also described an experiment in which two pigeons were fed arsenic, but the one who was given some scrapings of unicorn horn recovered and lived. The other died two hours after being fed the toxin [PDF].
But by the 17th century, the myth of the unicorn had begun to tarnish. European travelers to the Arctic brought back tales of the living narwhal, and further missions to other continents disproved the existence of unicorns by process of elimination, since no such animal was ever sighted. In July 1661, the men of the newly formed Royal Society put unicorn horn to the test: They placed a spider in a circle of powdered unicorn's horn to see what would happen. From from being repelled by the horn, as writers had long claimed, the spider immediately scurried across the powder to escape. The men repeated the experiment several times, each with the same results. Their trial helped sound the death knell for credulous belief in the magical properties of unicorn horn.
The loss of value resulted in the disappearance or destruction of many precious specimens. Items once said to be made from unicorn horn are still in some museum collections, and very occasionally turn up for sale—still bearing their historical value, though no longer imbued with the mysterious properties that once made them worth a city or a castle.