Turn on any fantasy movie or series and you are guaranteed to see monsters inspired by the medieval imagination.  Griffins, dragons, and unicorns have become commonplace in today’s media with the success of properties like The Lord of the Rings and Game of Thrones. While a handful of curious creatures have emerged as holdovers from the period, medieval thinkers envisioned bizarre and unusual animals that have faded into obscurity over time. Leaping forth from the pages of medieval bestiaries, compendiums of animal knowledge, these beasts provide insight into the way that western Europe viewed the world during the Middle Ages. This article will introduce you to the tradition of bestiary-writing, monsters you may never have heard of, and re-introduce you to some creatures that you may think you know.

What is a Bestiary?

Bestiaries were a genre of texts that provided information about animals to medieval readers.  Like much medieval knowledge, these bestiaries were in fact collections of lore accumulated from a variety of earlier sources.  This learning was pulled from Roman authors like Pliny the Younger and his Natural History, the Greek Physiologus, and Isidore of Seville’s Etymologies.

Such books were wildly popular throughout the Middle Ages and could be found in libraries across Europe. The bestiaries compiled animal knowledge and provided a Christian framework for understanding their world. Medieval readers interpreted the curiosities of nature as a representation of God’s will and extracted morals from them. While this is not how we study animals today, this perspective made sense of what we might perceive as bizarre and even contradictory ways of thinking.

A page from the Aberdeen bestiary book, featuring a variety of fantastical animals of various shapes and colors.
Detail from the 12th Century Aberdeen Bestiary depicting Adam assigning names to animals, Wikimedia Commons


It may seem strange to begin a survey of “monsters” with a real creature, but the medieval pelican was a much different creature than we know today. Many animals described in the bestiaries served as a kind of living representation for Jesus Christ and his resurrection. For this reason, they attributed some curious and even murderous behavior to many birds and beasts!

The second-family bestiary records that pelican chicks, “strike their parents in the face… but the parents hitting back kill them.” Though this infanticide is shocking, the bestiary provides a comforting resolution for the baby birds. On the third day after their death, the pelican mother uses its prodigious beak to tear open its own breast and pour blood onto the babies. Suitably drenched, the baby birds return to life in the same way that Christ was resurrected after his death on the cross. Such a Christian framework inspired every aspect of medieval thinking and helps us explain the strange ways they sometimes viewed animals.

An illustration from a medieval bestiary book depicting three scenes of a pelican being attacked and defending its offspring.
A narrative unfolds in three scenes – the offspring attacking the parent pelican, the parents retaliating to kill the young ones, and the mother pelican piercing her side to revive her offspring, The Aberdeen Bestiary


One of the more unusual creatures in these sources is the somewhat confusing Leontophone.

Lions were common sights in bestiaries, admired for their strength, majesty, and intimidating voices.  However, while the lion might be the “ruler of all beasts,” it was said to have a feared enemy: the leontophone. While details about the leontophone are somewhat hazy, with no consistent representation of its physical appearance, it was said to be a small creature that was perilous to lions. 

According to sources like the twelfth-century Aberdeen Bestiary, hunters could burn the remains of a leontophone and mix the ashes in with bait set out for lions, which killed them “even if they eat only a small amount.” Medieval writers believed that lions were aware of this danger, and tore these little beasts to shreds with their claws in order to avoid accidentally eating them!

An image from a medieval bestiary book depicting a lion and a small dinosaur-like creature call a leontophone chasing it.
A lion running away from a leontophone, a small creature known to be lethal to lions, Gossuin de Metz’s Image du Monde


Perhaps the most colorful and scatological medieval monster was the Bonnacon. This animal is described as having a body like a bull’s, but with a horse’s mane and horns that curled inwards. Originating in Asia, the bestiaries relate that the Bonnacon defended itself with an extreme case of explosive diarrhea.

According to the Aberdeen Bestiary, “when it turns to flee, it discharges fumes from the excrement of its belly over a distance of three acres, the heat of which sets fire to anything it touches.” It is unsurprising that medieval authors placed the Bonnacon and its burning excrement outside of Europe, depicting it on the fringes of maps like the thirteenth-century Hereford Map. Western medieval Christians often portrayed the east as a land of wonders and terrors in ways that set the stage for the orientalism of later generations. 

An illustration from a bestiary book featuring a bonnacon defending itself from two attackers by expelling explosive diarrhea at them.
The bonnacon shown to expel explosive diarrhea that burn everything around, The Aberdeen Bestiary

Unicorn and Monoceros

While we all know the majestic and dainty unicorn which adorns elementary school notebooks all over the world, many are not familiar with the similar but deadlier Monoceros. Although medieval writers could describe the unicorn as being quite ferocious, it had a weakness for certain young women. It was said that if a unicorn encountered a virgin, “it leaps into her lap and embraces her, and thus, it is seized” and could be captured. This scene became an iconic element of the unicorn’s legend and was frequently depicted in art from the period.

The monoceros, however, was something of an inverse of the unicorn. Said to be a chimera with “an equine body, feet like those of elephants, [and] a tail similar to a stag,” it also boasted an impressive “four foot horn.” Unlike the unicorn, which could be captured through virginal assistance, the monoceros’ horn could kill any beast while its howl struck terror into its foes. For this reason, it could never be effectively tamed or captured and could only be killed. While the monoceros has largely disappeared from modern culture, its legacy lives on in the scientific name of the narwhal (monodon monceros)!

An illustration of a monoceros, a mythical medeival creature with a stag's head, boar's tail, elephant's feet, horse's body, and a four-foot long horn on its head.
The monoceros features a stag’s head, boar’s tail, elephant’s feet, horse’s body, and a four-foot long horn, The Aberdeen Bestiary


Most readers are probably familiar with the basilisk from the Harry Potter series, but the creature loomed large in medieval Christian bestiaries. 

The creature, whose name was thought to come from the Greek basileus (ruler), was described as the “king of serpents.” According to some traditions, the basilisk could be created by alchemists by incubating a snake egg under a toad. Sometimes depicted as a serpent and sometimes as a rooster with a snake’s tail, both versions were equally frightening. 

Most sources describe the basilisk as killing creatures on sight through either its breath or its gaze, adding to the danger posed by this royal serpent and inspiring the petrifying abilities found in modern media. Despite this, weasels were said to be able to ferret out and destroy the basilisk because, “the Father of all things (God) never makes anything without a counterforce.” While the bestiaries imagined the world as filled with evil and danger, they had faith in divine will to balance the scales.

An illustration of a basilisk, a creature adorned with a raptor's beak, a cockscomb, wings, tail, and claws. The basilisk is being attacked by a weasel, who is bitting the basilisk's neck.
This basilisk, adorned with a raptor’s beak, a cockscomb, wings, tail, and claws, is under attack by a weasel, The Aberdeen Bestiary


I will end this discussion of medieval beasts with the most iconic of monsters, which took a very different shape in the Middle Ages.  The dragon was perceived by many medieval sources as an embodiment of evil, a representation of the devil himself.

In this early form, however, the dragon resembled not so much the fire breathing drake of Game of Thrones as real world snake. Described as the “larger than all serpents or than all animals on earth,” it was said to emerge from caves in India and Ethiopia and create a shimmering light as it flew through the air. This dragon was often a wingless and legless serpent which killed not with fire or with venom, but by winding itself around its prey like an anaconda.

Because bestiaries presented the dragon as the devil-incarnate, they were often set in opposition to animals who were representations of Christ. Its traditional foe was the elephant, a noble beast that the dragon snared with its coils, just as the devil set traps for man to sin. While a far cry from the dragons we know today, this beast set a precedent for such monsters as the archetypal villain of later fiction.

An illustration from a medieval bestiary book depicting an elephant with a dragon wrapped around it. The dragon is bitting the elephant's back.
A dragon attacking an elephant, The Aberdeen Bestiary


Consulting medieval bestiaries confronts the modern reader with a strange world of fantastical beasts. While we think of these monsters as fictional today, they were very real to the medieval readers of these texts and give us a sense of how they viewed the world. 

The medieval mind saw nature as a reflection of God’s will and took deep metaphorical and allegorical meanings from it. Yet this world was also a dangerous place, in which far-off lands housed bizarre and frightful creatures. From the bonnacon to the basilisk, these animals illuminated a divine order to the universe that set good and evil in stark opposition. In this way, they not only delight the modern imagination but give us a sense of the creative mindset of people who lived hundreds of years ago.