Alicorn: how a narwhal's tooth became a unicorn's horn
The word for a unicorn's horn is alicorn, and for most of the Middle Ages and the Renaissance it was one of the most expensive substances in Europe — worth, by some accounts, ten times its weight in gold. Kings kept pieces of it in their treasuries. Apothecaries sold shavings of it as medicine. The catch, which almost nobody in the trade seems to have known, is that it did not come from a unicorn. It came from a whale.
The narwhal is a small Arctic whale, and the males grow a single long, straight, left-handed spiral tusk — really an enormously overgrown tooth — that can reach three metres. Inuit hunters in Greenland and the Canadian Arctic took narwhals for meat and ivory, and the tusks moved south along trade routes until they reached Europe, where nobody had ever seen the animal. What arrived was a beautiful spiral horn with no beast attached. The obvious explanation, to a medieval mind steeped in bestiaries, was that it belonged to the unicorn.
The Norse, and later Danish and Hanseatic merchants, understood the value of keeping the source a secret. A horn was worth a fortune precisely because it was believed to be rare and magical; explaining that it grew in the mouth of a whale would have collapsed the market overnight. So the story held for centuries.
An "alicorn" was believed to sweat, or crack, in the presence of poison — which made it very interesting to anyone who dined with enemies.
Its supposed powers were mostly about poison. A cup carved from alicorn, or a horn dipped into a drink, was thought to neutralise venom or at least reveal it. For a Renaissance prince who genuinely expected to be poisoned, that was not a superstition to economise on. The horn of the "unicorn" at the French court, and the spiralled staff you sometimes see in portraits, were security equipment as much as ornament. Powdered alicorn also turns up in pharmacopoeias as a treatment for fevers, plague and epilepsy, sold by weight at ruinous prices.
The unravelling was gradual. As European ships pushed into northern waters in the sixteenth and seventeenth centuries, more people saw narwhals, and naturalists began to connect the tusk to the animal. The Danish physician Ole Worm is often credited with demonstrating, in the 1630s, that the celebrated horns were narwhal teeth. Even then the belief was sticky: a thing can be known to be a whale's tooth and still be sold, and paid for, as a unicorn's horn, because the price was never really about zoology.
What I like about this story is that the myth and the animal were both real; they were just attached to each other by a long supply chain and a convenient silence. Somewhere out in the cold, the actual owner of the horn went on with its life, unaware that it was propping up half the magic of European courts.