In medieval Scandinavian sources, a berserker is a viking warrior fighting in a frenzy, who does not perceive any pain or wounds. This type of warrior, who fought on the side of various Germanic tribes, is also reported by Roman sources in the imperial period. However, they are not called "berserkers" there, but have other designations.
The word berserk is a word of Old Norse, formally a compound noun. The second part serkr is unanimously interpreted as "garment, tunic".
Concerning the first component there are different assumptions, two of which are discussed: On the one hand, a connection with a word for bear is considered, although this is bjorn in Old Norse.
On the other hand, other experts argue that according to the descriptions, the berserkers were light-footed folk and therefore a comparison with bar "bare, free" is more appropriate.
Today it is rather assumed that the term is taken from the frenzy (or "battle frenzy", berseksgangr, Latin furor germanicus) to fight like a bear or wolf.
This is associated with the transformations often described in the Nordic sagas, which are also known here in connection with the werewolf.
From stanzas 20, 21 of Haraldskvæði, it can be seen that the berserkers fought in principle in the first line of any battle order and there without regard to casualties. However, they are remarkably rarely mentioned in the battle reports.
Klaus von See probably thought that stanzas 13-23 are an addition from the beginning of the 12th century, so that only the stanza mentioned above is from the 9th century.
250 years passed before the word "berserker" is mentioned again in literature. From this Klaus von See concludes that it was not a fixed contemporary term, but a word creation of the poet Þorbjörn hornklofi, whereby he took over the word combination with "ber-", which otherwise does not occur in Scandinavian literature, from German originals, and adds two further word combinations with "ber-" "ber-harð" (bear-hard) and "ber-fjall" (bear-skin, not, as expected, "bear-rock") by Þorbjörn, which he borrowed from the German vocabulary. The word "berserkr" becomes common only in the 12th century.
The animal warriors often appeared in closed groups, as in the account of the Battle of Hafrsfjord cited above. The sagas consistently report that the berserkers were positioned at the bow of the ship, i.e., the most dangerous place during battle.
They were considered an elite royal force. Their number is usually given as twelve. But it is wrong to call the berserkers only "elite warriors".
Rather, berserkers are people with special characteristics, who appear in the sources sometimes as elite warriors, sometimes as henchmen of powerful rulers, sometimes as dangerous criminals, also as brigands and also as sorcerers.
They occur in most distinguished families, but are also family-less forest people.
After Christianity was established around 1025, there were no more berserkers. In the Icelandic Christian law of 1122 (chap. 7 of the Grágás) it is forbidden to go into a berserker rage, although it is not certain that this refers to the literarily attested berserker gait or not simply a rampage.
In the Norwegian Christian laws of this time, berserkers are no longer mentioned. Both indicate that this fighting style was already on the wane or had already disappeared by this time, albeit with regional variations.
After that, two strands of tradition emerge: one calls particularly brave warriors berserkers without attributing any special characteristics to them, the other begins to stylize them as human beasts.
Common to both strands is that the authors had no own view of berserkers and also knew no living witnesses who had experienced berserkers themselves. The berserkers were known only from hearsay.
The Grettis saga, written only around 1320, belongs to the first strand of tradition. It already considers particularly brave men to be "berserkers". In contrast to all older reports, it already considers the leader of Harald's opponents to be a berserker when describing the battle at Hafrsfjord.
A group of berserkers was considered capable of turning the tide of battle. Due to their ruthless approach and, according to the lore, the greatly reduced to completely neutralized sense of pain, they were able to perform decisive, but also bloody maneuvers for both sides.
In the Hrólf Krakis saga, there is much talk of berserkers sitting beside the king. But in this late 14th century story, the berserkers are far from invulnerable, nor do they have any other unusual abilities. In the story of Halfdan, the protege of Brana, the terms "berserker" and "Viking" are even used synonymously.
The stylization of berserkers as human beasts finds its earliest literary expression in Saxo Grammaticus. Snorri Sturluson, who lived later, is in the same tradition in some texts.
The berserker was now thought to have special qualities: He was impervious to fire, and iron swords did not wound him. The berserker rage began with trembling, coldness of the head and chattering of teeth (apparently similar to chills), sometimes the head swelled and the color of the face changed, followed by loud roaring and biting into the shield. It is considered whether this biting into the shield may have had magical significance.
The descriptions of the berserker's rampages in Saxo Grammaticus and Snorri inspired many to attempt explanations.
Samuel Lorenzo Ödman, a theologian at the University of Uppsala, was the first to develop the theory that the berserker attack was due to the ingestion of toadstools.
He was guided by news about the use of fly agaric among the shamans of Siberia, without having made any observations himself about the mode of action of fly agaric. However, muscarinic syndrome does not lead to an increase in fighting strength.
Moreover, the amount of muscarinic contained in fly agaric is too small to cause such a syndrome. The primary toxins, muscimol and ibotenic acid, have sedative and hallucinogenic effects, not drive-enhancing or analgesic effects. The theory is no longer held.
When LSD was isolated from ergot, ergot also came under temporary discussion as a causative agent.
Later, marsh spurge was also considered as an ingredient in beer during the Viking Age. Sandermann, who was probably the first to discuss this plant in the literature, asks in his essay Berserkerwut durch Sumpfporst-Bier why, with such a wide distribution of beer, so few people have survived as berserkers.
Elsewhere, Rätsch says there is only one substance that makes people really aggressive, and that is alcohol.
There is no known scientific study that has found substances from plants that occur in Scandinavia as probable triggers of the described berserker rage attacks.
In Scandinavian medical history, berserk rage is predominantly seen as a psychopathic phenomenon, perhaps linked to a certain predisposition.
Thus, the linking of berserkers with wolf-men is given greater attention in the sources and is associated with the concept of lycanthropy. "Sacred frenzy" as a classical initiation rite has also been considered.
Høyersten considers the phenomena described to be a dissociative trance, an autohypnosis. Biting the shield, sometimes in groups, was said to be the initiation ritual triggering the self-suggestion.
The clinical picture of such self-suggestion included impaired perception of the environment with decreased sensitivity to pain and increased muscle strength. Critical thinking and general inhibitions are weakened. This state is followed by a mental discharge in the form of fatigue, exhaustion, often followed by sleep.
A final clarification is hindered by the fact that the news about the berserker's walk was written at a time when there had been no berserkers for generations. Thus, they are not direct eyewitness accounts of the rampage. None of these theories, therefore, has yet found favor with historians.