There were few established military institutions in Scandinavia at the start of the Viking Age, circa 800, but a number of such organisations gradually developed as society came increasingly under the rule of a single king. The foremost institution was the retinue, a brotherhood of warriors serving a common master. It developed to become the main source of power for the medieval kings and evolved into a noble elite in the Middle Ages.


But there was a more sinister brotherhood of warriors in Scandinavia that could not find any place in the post-heathen world of Christianity. Instead it only survived in the realm of the sagas, the art and the folklore, often becoming shield-biting demons of war and symbols of evildoing. But behind the myth and the shroud of history, the sources reveal the existence of men thriving on the border between life and death, fuelled by war and distinguished by their ecstatic battle fury.

The description of ‘berserkers’ and ‘wolfskins’ in the sources is on the boundary between fantasy and reality, and it is difficult for us today to imagine that such people can have ever existed, possessed of incontrollable destructive power. But they did. The berserkers and the wolfskins (also known as ‘heathen wolves’) were a special group of very skilled and dangerous warriors associated with the god Odin.

Vikings: Valhalla – the real history behind Netflix's successor to Vikings

Netflix's Vikings: Valhalla brings a new generation of Viking schemers and dreamers to the screen, from explorers Leif Erikson and Freydís Eiríksdóttir to warrior Harald Sigurdsson and empire-builder King Cnut. Here’s what’s what to expect from the show, plus the real history that underpins the story

Leif Erikson in Vikings Valhalla

How might berserkers have fought in wars?

If there were elite troops such as berserkers and wolfskins available on the battlefield, they were put in the front of the phalanx [a rectangular mass military formation, usually composed entirely of heavy infantry] to resist the main weight of an attack, or at the front when launching an attack. But berserker troops could be a double-edged sword, as they were difficult to control in a battle and were often ill-suited to formation warfare. Instead, they seem to prefer to operate in smaller groups, attacking independently. Olav Haraldsson (St Olav) put the berserkers in front of his own phalanx at the battle of Stiklestad in the year 1030, but instead of holding the line they attacked and thereby contributed to the king’s downfall.

This marginal illumination from the Saga of Saint Olaf shows his death at the battle of Stiklestad in 1030.
This marginal illumination from the Saga of Saint Olaf shows his death at the battle of Stiklestad in 1030. (Photo by Werner Forman/Universal Images Group/Getty Images)

Viking warriors looked to the god Odin to give them aggression and courage in battle, but the berserkers took this a step further. According to the sources they could rout an outnumbering force, and when they attacked they howled like mad dogs or wolves. It was said that neither iron nor fire could injure them, and they didn’t know pain. After a battle they were as weak as infants, totally spent both physically and psychologically.

More like this

It is difficult to find any clear difference between a berserker and a wolfskin. Sometimes they appear to be the same, under the general description of berserker, and at other times they are portrayed as two different types of warrior. In some contexts, the wolfskins are even more closely connected with the Odin cult than the berserkers seem to be.

A brotherhood of war

Originally berserkers developed their own brotherhood of professional warriors who travelled round and took service with different chiefs. What distinguished them was that they had bears and wolves as totem animals, and clad themselves in their skins. Irrespective of whether it was a bear or a wolf, the warriors believed they were endowed with the spirit of the animal. Designs showing warriors clad in what could be bearskins occur, among other places, on the Torslund plates from Öland, thought to date from the seventh century.

In the Fornalder sagas (‘Sagas of Earlier Times’) and in several other sagas, the king’s or the chieftain’s guard is described as made up of berserkers, usually 12 in number. The berserkers often comprised an elite troop in addition to the guard or the army in general. In sea battles they were usually stationed at the prow, to take the leading point of an attack. In the battle of Hafrsfjord, c872, they appear as shock troops for Harald Hårfagre (Finehair), in groups of 12.

The berserkers are spoken of as fearsome enemies to meet. They were often said to be so intoxicated by battle-lust that they bit their shields, attacked boulders and trees and even killed each other while they were waiting for battles to begin. A set of chessmen from the 12th century found on the Isle of Lewis in the Scottish Hebrides includes a chess piece of a warrior biting his shield.

The title of berserker is thought sometimes to have been inherited from father to son, and there are known examples of entire families of berserkers. One such family known from the sagas is Egil Skallagrimson. Egil’s father, Skallagrim (‘ugly skull’), and his grandfather Kveldulv (‘nightwolf’) were also berserkers.

The concept of ‘berserk’ also turns up independently of ‘berserker’. The idea of ‘going berserk’ could apply to more than just the members of a warrior brotherhood. Harald Hardråde (Hardruler) “went berserk” at the 1066 battle of Stamford Bridge, for example. The expression is also used in relation to warriors who are not thought to have been wearing any distinctive uniform of animal skins. Olav Haraldsson’s berserkers, who wrecked the battle of Stiklestad for him, are an example of this.

25th September 1066, King Harold II (c.1020 - 1066), the Saxon king of Britain beholds the body of his rebellious brother Tostig, whom he has just defeated at the Battle of Stamford Bridge, Yorkshire. Next to Tostig lies his ally, King Harold III (1015 - 1066) or Hardrade of Norway. By D. Maclise. (Photo by Hulton Archive/Getty Images)
King Harold II, the Saxon king of Britain, beholds the body of his rebellious brother Tostig, whom he has just defeated at the battle of Stamford Bridge, 1066. (Photo by Hulton Archive/Getty Images)

What's the earliest evidence of berserkers?

The earliest written sources of what might be berserkers are found in Roman writings from the first century AD. In his book Germania, the historian Tacitus describes correspondingly fantastic elite warriors among the German tribes in northern Europe. In the sixth century, the East Roman historian Prokopios wrote of “the wild and lawless heruli” from the north, describing how they went almost naked into battle, clad only in loincloths – this was to show disdain for their wounds. They wore neither helmet nor coat of mail, and used only a light shield to protect themselves. The people who were described as ‘heruli’ probably had their origin on Sjæland or Fyn in today’s Denmark, but they can also be traced to other parts of Scandinavia, including Norway.

The heruli are said to have had a kingdom on Fyn. This may have survived until into the sixth century, but more of them had previously been driven out of Scandinavia by the Danes. The heruli often took service as warrior bands in the Roman army. They appeared in the same way as the berserkers, in small groups in the service of chieftains or kings, and there is a possibility that the origins of the berserkers may be found among the mysterious heruli.

The Vikings | A short course from HistoryExtra Academy

Member exclusive | Join Professor Ryan Lavelle for our four-week course on the Vikings – from trading and exploring to daily life.

Explore the course now

The berserkers are often mentioned in sagas, skaldic poems [composed at the courts of Scandinavian and Icelandic leaders during the Viking and Middle Ages] and other literature from the Middle Ages. In the sagas, which were written in a Christian context, the memory of these warriors has been extended to become a label for those who stand out from the norms of society: thugs and freebooters, pirates and so on. In the earliest Icelandic compendium of law, Grågås, it is said that a raging berserker can either be bound or condemned to exile.

The oldest known written source about berserkers is Haraldskvadet, a 9th-century skaldic poem honouring King Harald, attributed to the skaldic poet Torbjørn Hornklove. Writing about the battle of Hafrsfjord [date unknown], he writes: “Berserkers roared where the battle raged, wolf-heathens howled and iron weapons trembled”.

The Battle of Hafrsfjord. Image shot 1754. Exact date unknown.
Battle of Hafrsfjord. (World History Archive/Alamy Stock Photo)

In Grette’s Saga it is said of the warriors in that same battle: “… such berserkers as were called wolf-heathens; they had wolf-coverings as mail… and iron didn’t bite them; one of them… started roaring and bit the edge of his shield… and growled viciously”.
In the Volsung Saga, describing events in the sixth century, it is said that the berserkers were in Odin’s lifeguard and that they “went without armour, were as mad as dogs and wolves, they bit their shields, were as strong as bears or oxen, they killed everybody, and neither fire nor iron bit them; this is called going berserk”.

The descriptions in the sagas of violent men and killers cannot all be linked to the berserkers, however. Distinctions are made, for example, between ‘berserkers’ and ‘warriors,’ and between ‘normal’ killers and men who fought duels. And the Old Norse saga texts never call the berserkers mad or insane. They regard the berserkers as something more than just socially problematic and unusually aggressive. The sagas distinguish them from other men by ascribing to them a particular ‘nature’ that made one both scornful and fearful of them at the same time.

'Going berserk': what's the mushroom theory?

In 1784 a priest named Ödmann started a theory that ‘going berserk’ was the result of eating fly agaric mushrooms (Amanita muscaria). That explanation gradually became more popular, and remains so today. Ödmann based his hypothesis on reports about Siberian shamans, but it is important to note that he had no personal observations of the effects of eating this type of mushroom.

White agaric has also been suggested as a cause of the berserk fury, but considering how poisonous this is, it is quite unthinkable that it would be eaten. Eating agaric mushrooms can lead to depression and can make the user apathetic, in addition to its hallucinogenic effects. Berserkers are certainly never described as apathetic!

Poisoning with the fungus Claviceps purpurea has also been suggested – it contains a compound used to synthesise the hallucinogen LSD (lysergic acid diethylamide). However, if mushrooms had been so important for the berserkers, they would surely have been mentioned in the sagas, which they are not.

The most probable explanation for ‘going berserk’ comes from psychiatry. The theory is that the groups of warriors, through ritual processes carried out before a battle (such as biting the edges of their shields), went into a self-induced hypnotic trance. In this dissociative state they lost conscious control of their actions, which are then directed subconsciously. People in this state seem remote, have little awareness of their surroundings and have reduced awareness of pain and increased muscle strength. Critical thinking and normal social inhibitions weaken, but the people affected are not unconscious.

Flora, Fauna, Fungi, Amanita Muscaria, red large wild mushroom.
Fly Agaric mushroom. (Photo by Eye Ubiquitous/UIG via Getty Images)

This condition of psychomotor automatism possibly resembles what in forensic psychiatry is described as ‘diminished responsibility’. The condition is followed by a major emotional catharsis in the form of tiredness and exhaustion, sometimes followed by sleep. Researchers think that the short-term aim of the trance may have been to achieve an abreaction of strong aggressive, destructive and sadistic impulses in a socially defined role.

The Old Norse social order and religion were able to accommodate this type of behaviour, and it is understandable that the phenomenon disappeared after the introduction of Christianity. A Christian society considered such rituals and actions as demonic and thought that they must have resulted from supernatural influences.

More from us

HistoryExtra members can explore this topic further with exclusive content from our archives

Not a HistoryExtra member? Explore our latest membership offers

Kim Hjardar is the co-author, with Vegard Vike, of Vikings at War, which will be published in hardback in October by Casemate Books.


Hjardar holds a MPhil in Nordic Viking and medieval culture from the University of Oslo and works as a lecturer in history at St Hallvard College. He is also archaeological conservator at the Museum of Cultural History, Oslo.

This article was first published on History Extra in September 2016