Berserkers: Bear Shirts, Mushrooms, and the Truth Behind the Myth

"He went completely berserk." Hardly any Old Norse word has become as everyday as this one. It stands for outbursts of rage and loss of control, and it goes back to a group of warriors who appear in the Norse sagas: the berserkers. Bear pelts, shield-biting, mushroom frenzy, invulnerability: the picture we have today is a cocktail of real sources, later embellishment, and a theory from the 18th century.

This article sorts out what is really in the sources, what was added later, and what has been circulating for centuries without ever being documented.

In short: according to the Norse sources, berserkers were warriors who fought as if out of their senses, appeared in animal skins, and were associated with Odin. The earliest mention appears in a poem around 900 about King Harald Fairhair. There is no source that connects their frenzy with mushrooms or drugs. They were banned in Norway in the 11th century, and by the 12th century their organized groups had vanished.

The Old Norse "berserkr" is made up of two parts. "Serkr" means "shirt." The first part, "ber," is where it gets interesting: the most common reading takes it as "bear," making the word "bear shirt," someone in a bear pelt. Snorri Sturluson, the Icelandic scholar of the 13th century, read it instead as "bare," meaning naked, and understood it as warriors who fought without armor.

Scholarship has swung back and forth over the decades. The "bare-shirt" reading was long considered superseded in the 19th century but came back into fashion between the world wars. Today "bear shirt" is considered more likely, not least because it fits a whole family of animal warrior names. All that's certain: whoever called himself a "berserker" wore either a bear pelt or no armor, and some sources hint that both could be meant at once.

The oldest surviving mention is in the "Haraldskvæði," also called the "Hrafnsmál" ("Raven Song"), a praise poem by the court poet Þorbjörn Hornklofi for King Harald Fairhair of Norway, composed around 900. It describes the Battle of Hafrsfjord, in which Harald defeated his opponents, and names berserkers among his warriors. In doing so, it uses a second word: "úlfheðnar," "men in wolf skins." Harald Fairhair is, incidentally, the father of Eric Bloodaxe. That we know the poem at all we owe to Snorri, who transmitted it in the 13th century, and that means almost all our berserker images run through the same author.

That matters because it shows this was not about a single bear pelt. There was a whole family of animal warriors: bears, wolves, and in some accounts boars. The wolf-skin warriors also appear in the Vatnsdœla saga and the Völsunga saga. Everything else about them is considerably younger, a large part from the 13th century, about 400 years after the Viking Age.

The best-known description comes from Snorri Sturluson in the "Ynglinga saga" (13th century). Odin's men, he writes, went into battle without armor, were as wild as dogs or wolves, bit their shields, and were as strong as bears or bulls. They killed with a single blow, yet neither fire nor iron could harm them. This is the source of almost all berserker clichés, from shield-biting to invulnerability.

A completely different trail leads to Sweden. In 1870, four bronze dies from the Vendel period (6th or 7th century), used to stamp thin images for helmets, were found at Torslunda on the island of Öland. One shows an apparently one-eyed dancer in a helmet with bird-head horns beside a warrior in a wolf pelt holding a spear. Many researchers read that as a scene from the circle of the Odin cult and battle frenzy, others consider the interpretation disputed. The find offers no more than a hint: it shows warriors in animal skins, but no battle frenzy.

The sagas describe a state they call "berserksgangr," literally the "going of the berserker": a battle frenzy that let strength grow and pain vanish. Afterward, the tales say, the warriors were exhausted and drained. In Egil's saga, a band accompanying the later Skalla-Grim is described as "the hardest of men," with "a touch of the uncanny" about some. Egil's grandfather bore the name Kveld-Ulf, "Evening Wolf." In the saga of Hrólf Kraki, men see a great bear going before the king's warriors, always keeping close to the king.

Shield-biting appears over and over in the sagas and is read as a sign of fearlessness or madness. What is poetry and what is observation can't be separated: all these accounts were written down centuries after the events, by Christians who saw some of these warriors as figures of a pagan past. That they were invulnerable belongs to poetry: they could be wounded and killed, and in the frenzy it may only have looked as if they felt nothing.

In 1784, the Swedish theologian and naturalist Samuel Ödmann proposed that berserkers had eaten fly agaric mushrooms (Amanita muscaria), modeled on Siberian shamans. The idea became extremely popular and still appears in documentaries and books. There are three problems: no Old Norse text mentions mushrooms or a potion in connection with the berserksgang. Ödmann reasoned from an analogy, around 700 years after the Viking Age. And the typical effect of fly agaric, drowsiness, confusion, and nausea, is a poor recipe for coordinated shock troops.

Ödmann's model, the use of fly agaric among Siberian peoples, had only been described in Europe in 1730. In 1956, an article by Fabing revived the theory, and at times it found broad acceptance among Scandinavian scholars. Fly agaric has also never been found in Viking Age graves or ritual contexts. The theory persists mainly because it offers a simple explanation for a puzzling phenomenon, not because evidence underlies it.

The alternative, by contrast, has a find behind it: seeds of black henbane (Hyoscyamus niger) were discovered in a Viking grave near Fyrkat in Denmark, first described in 1977. It is the grave of a 10th-century woman, probably a seeress, with the seeds in a leather pouch. Fyrkat was a ring fortress that Harald Bluetooth had built around 980. The seeds prove that the plant was known and used. Henbane was also used in Europe to flavor beer, until hops displaced it between the 11th and 16th centuries, and Bavaria's Purity Law of 1516 allowed only barley, hops, yeast, and water.

In 2019, Karsten Fatur concluded in the Journal of Ethnopharmacology that henbane explains the described symptoms of the berserksgang better than fly agaric. But here too: that is a fit of symptoms, not proof. There is no sign that a berserker ever took henbane. The Fyrkat find shows a seeress with the plant, not a warrior. Summed up honestly: berserker rage might also have been a ritual, a trance, alcohol, or pure psychology. According to one account, fly agaric or alcohol severely reduced fighting ability, which is why some assume the frenzy was produced psychologically, for example through rituals and dances.

With Christianity, the view of these warriors changed. According to Grettis saga, Jarl Eiríkr Hákonarson of Norway banned both berserkers and duels shortly before leaving for England, traditionally 1015. The saga was written much later, though, so the date is tradition. The Icelandic law code Grágás later punished "going berserk" with lesser outlawry, a form of banishment.

By the 12th century, organized berserker groups had disappeared. What remained was the word, and over the centuries it became what we mean today: a person who loses control.

One detail hardly anyone knows: the Book of Ceremonies of the Byzantine court describes a "Gothic dance" performed by members of the Varangian Guard, those Norse warriors in the emperor's service. They appeared in animal skins and masks. Some researchers see in it a late echo of the animal-warrior tradition, in the heart of the Byzantine Empire, far from Norway and Sweden.

It shows how long the image of the animal warrior lasted, even after real berserker bands had long disappeared. The pelt remained as a sign, even when the frenzy was only a memory.

To quickly check the berserker clichés, here are the main claims with what the sources actually offer.

To wrap up, the short version, so fact and story don't blur.

Berserkers show why an era needs more than names and battles. That's why every season in HistoryBytes is split into five categories, and this story touches all five: Harald Fairhair as a person, Hafrsfjord as a place, the battle as an event, the battle frenzy of the berserksgang as an idea, the Torslunda dies as an object. That's how the Viking Sagas season builds the whole picture of a time, how people lived, believed, and fought.

In the end there's an irony: we know remarkably little about the berserkers, but their name accompanies us every day, in every outburst we call "berserk." What remains is a mosaic: a poem around 900, bronze stamps from Öland, a grave at Fyrkat, and a dozen sagas written centuries after the events. It's enough to know that there were warriors in animal skins who were associated with Odin. It's not enough to know what they did or felt in the moment before they struck.