Cases of poisoning fascinate and terrify us in equal measure. This has been very apparent in recent weeks, given the extent to which the attempted murder in Salisbury, England of Sergei and Yulia Skripal—a former Russian double agent and his daughter—has caused international political uproar and caught the media imagination. The poisoning is just the latest installment in a long series of politically-motivated poisonings which have been linked to the Russian state. In the 1950s, KGB defector Nikolai Khoklov was poisoned with thallium; former Ukrainian president Viktor Yuschchenko survived an attempt on his life in 2004; in 2006, FSB officer-turned-Kremlin critic Alexander Litvinenko was murdered using a dose of the radioactive substance polonium.

Police now believe that the Skripals were poisoned by a military-grade nerve agent which was smeared on the front door of their home, something which has added an extra frisson of unease to the horror. No one likes to think of something so lethal and yet so undetectable contaminating the one place—the home—where you should feel safe. Understandably, many of the inhabitants of Salisbury have been unnerved by the possibility that the places where they live and work might have been contaminated, and local businesses have struggled to cope as people avoid the town. That anxiety—about poison and the difficulty of detecting it—has a long history, particularly when it comes to the European Middle Ages.

A woman carrying flasks of poison. A 13th-century stained glass panel showing a scene from the legend of St Germain. [Met Museum]

Leaf through any book on medieval politics, and you’ll come across the names of dozens of people who are supposed to have met a grisly end because of the poisoner’s art. Henri of Flanders (d. 1216), the second Latin emperor of Constantinople, and Blanche II of Navarre (d. 1464) were both supposedly poisoned by members of their own families. This was also the case for Robert IV of Artois, count of Eu, and his wife Joanna of Durazzo, who paid a visit to Joanna’s sister Margherita, Queen of Naples, in 1387. Neither of them would leave the royal residence of Castel dell’Ovo alive, and people whispered that Margherita had wanted it that way.

Dmitriy Yurievich Shemyaka, twice Grand Prince of Moscow, however, irritated the Muscovites rather than his family members. In 1453, the city’s inhabitants bribed the prince’s cook to poison his roast chicken dinner. Other poisonings of high-ranking individuals remain unsolved: the Irish peer James Butler, earl of Ormond and a cousin of Anne Boleyn, died in London in 1546 as the apparent victim of poisoning along with seventeen other members of his household.

How many of these deaths, if any, were actual pre-meditated poisonings? At this remove, it’s almost possible to say. Medieval understandings of disease were imperfect, and they had a poor understanding of food hygiene. It’s not surprising that medieval people were quicker to suspect that an enemy had laced their food with hemlock, say, or wolf’s bane, or even the grandly named “Composition of Death” (a noxious mix of red copper, nitric acid, verdigris, arsenic, oak bark, rose water and black soot) than they were to imagine that a cook’s unwashed hands were to blame for a sudden illness or death. Moreover, there’s a fine line between medicine and poison—as attempts at creating medieval-themed gardens have shown, what can cure you in a small dose can kill you in a slightly larger one. An attempt to cure a minor case of food poisoning might have been enough to finish someone off.

The Byzantine Empress Zoë orders the poisoning of the eunuch John the Orphanotrophos. [Biblioteca Nacional de España, MS 234 h. perg. ]

Medieval people certainly thought that deliberate poisoning was a risk they faced, particularly when power and politics were involved. Such incidents might not have been as common as they thought, but they surely happened—after all, if you did poison someone, and carry it out discreetly, it could leave far fewer visible signs than a knife in the back. This concern with discretion means that a common trope in medieval-themed pop culture, the use of poison rings (rings whose bevel hides a compartment containing small quantities of poison to sneak into a rival’s food or drink) is almost certainly a medievalist fantasy. While archaeologists in Bulgaria claim to have found one during the excavation of a fourteenth-century fortress, and Cesare Borgia, son of Pope was reputed to have used one containing “cantarella”, a putrid and lethal mix of arsenic and ground-up insect, there’s little real evidence for the use of such rings. (And let’s face it, if your goal is to be undetected, these rings aren’t going to help.)

Surviving medieval artefacts that have firm links to poisoning have more to do with fear and attempts at prevention than they do with the delivery of poison. Limestone excavated from one particular cave on the island of Malta was thought to neutralise poison; it was powdered and fashioned into “contra veleno” drinking cups. “Unicorn” horn—in reality the tusk of the narwhal, a large Arctic sea mammal—was also thought to be efficacious against poison. It was ground into a powder that could be added to food or drink, or fashioned into protective amulets like the Danny Jewel. Shark’s teeth were believed to have the same effect, and were often used to decorate drinking goblets.

This object, made out of shark’s teeth and red coral, was reputed to change colour in the presence of poison. [Vienna, Treasury of the German Order.]

The best evidence about medieval attitudes towards poison, however, comes from written sources, which discuss where poisonous substances come from and how to deal with them. For example, the mandrake plant is best known to most people nowadays from the fantastical version of it which appears in the Harry Potter series of books. Its roots can look like a human body, and this led medieval people to believe that the body could come in male and female form. They believed that the plant sprang up anywhere that that fat, blood, and semen dripped from the body of a hanged man. Try to pull the mandrake from the soil, so the folklore goes, and will let out a piercing scream that will kill anyone in earshot. None of this is true, though given that the mandrake is a member of the deadly nightshade family of plants, eating it is likely to give you at the very least a nasty case of gastrointestinal distress. (It will also make you very sleepy, and so both the ancient Greeks and medieval Europeans employed it as a kind of makeshift anaesthetic. Don’t try this at home, though; even a little too much can send you into a coma.)

Blood was also thought to be a means of transmitting poisonous impurity—an example of a medieval theory that’s got a kernel of truth to it even if their understanding as a whole was flawed. Medieval Europeans believed that ox blood mixed into an omelette was invariably deadly, and that if a woman put some drops of her menstrual blood into her husband’s food, then the man would “die after one day or some days, or suffer what is far worse than death, namely suppurating elephantiasis.”

Sometimes a poison could be the means of its own cure. For instance, toads and frogs were a popular shorthand for pestilence in the Middle Ages, thanks to their use as metaphor in scripture. (The Book of Revelation describes devils as looking like frogs.) The twelfth-century writer Gerald of Wales even told a grisly story about tree-climbing, carnivorous toads with a taste for human flesh. Toads, however, could also be used to neutralise a poison. Medieval people believed that inside the head of elderly toads was a substance called a “toadstone”. A toadstone grew hot, changed colour, or sweated when it was near a poisonous substance, and so it could be set into a ring, like your own personal, life-changing mood ring. (How did you know if you had a real toadstone in your possession? Just hold it up in front of a live toad, which would leap towards it if genuine. Only a cynic, of course, would point out that toads are liable to hop in lots of different directions.)

The harvesting of a mandrake, from a 13th-century medical manuscript. Austrian National Library, Codex Vindobonensis 93, fol. 118r.

Medieval medical knowledge about poison may have limited applicability nowadays—eating citrus fruit has lots of health benefits, but we know now it won’t cure you if you’ve been poisoned—but are there other lessons we can learn from the Middle Ages about how to react in the face of such invisible threats? As international tensions ratchet upwards, with diplomats expelled and consulates closed, can we benefit from thinking about how accusations of poisoning were deployed in the distant past?

Well, we could pay attention to how accusations of poisoning could be hurled by those with economic motives against people who were socially disadvantaged—for example, the case of Margarida de Portu, who was living in the southern French town of Manosque in 1397 when she was accused by her brother-in-law Raymon of having poisoned her recently-deceased husband using a dish of lentils and garlic. It’s likely that the litigious Raymon wanted to disinherit Margarida, an immigrant to the town who had no nearby family to support her. More crucially, perhaps, we can think about how accusations of poisoning were frequently levelled against members of minority communities in the Middle Ages. When the Black Death struck Europe in the 1340s and 1350s, fear of this devastating illness combined with pre-existing anti-Semitism led to many Christians accusing Jews of deliberately spreading the infection by poisoning the water supply. Earlier in the fourteenth century, lepers in what is now southwestern France were accused of spreading that disease by poisoning wells, a nonsensical accusation which gained rapid currency because of the rumours that the lepers were in league with French Jews and foreign Muslim rulers.

A bad fate for a bad king? As early as the 13th century, tales circulated that King John of England had been poisoned to death by a monk (seen here offering him a poisoned chalice). British Library, Cotton MS Vitellius A XIII, f. 5v

In other words, part of the reason why poison is such a useful political weapon is because it can kill effectively—and because even the suspicion of its use can spread fear and mistrust among your political opponents. Russia exploited that long history, dating all the way back to the Middle Ages and beyond, when it chose to deploy an invisible, deadly poison on a quiet suburban street in England.