“As North American Indians had their distinct warrior societies, so Ancient Indo-Europeans had distinct warrior groups with their own customs and “willfulness.” The Sanskrit word swadha (“inherent power, habitual state, custom”) is the same word etymologically as Greek and English ethos and the Latin sodales (“men of an organization”). Berserks would have formed such groups.

To do deeds of berserk daring, one had to be raging mad. Homeric warriors fought best in a powerful rage, and Gaulish warriors could not help falling into the grip of battle madness. Shouting and singing were ways to rouse such rage. Early Greek and Roman warriors screeched like flocks of raucous birds—a mark of manhood. With a song of thunder and wind, the young Marut warriors of the Rig Veda awakened Indra’s prowess. Husky Thracian, Celtic, and Germanic war songs, like crashing waves, heartened warriors.

Dance emboldened even more. Not only Tukulti-Ninurta’s berserks danced on the battlefield; Vedic Indians did the same. Indra and his band of Marut warriors danced adorned with golden plates. Greek and Iranian warriors likewise danced, and to Hector battle itself was dance. Ancient Thracians danced on the battlefield, and so did naked Celtic warriors, wearing only golden neckbands and armrings. In Caesar’s time Romans still danced with weapons in hand, albeit no longer as soldiers but as teams of Salian priests. Dances, though done by all early warriors, mattered particularly to berserks as they fanned their fury.

Germanic warriors, too, danced on the battlefield. Tacitus describes the dance of their young, naked warriors thus:

They have only one kind of show and it is the same at every gathering. Naked youths whose sport this is fling themselves into a dance between threatening swords and spears. Training has produced skill, and skill, grace, but they do it not for gain or pay. However daring their abandon, their only reward is the spectators’ pleasure.

Both Indo-European war dances and images of early medieval war dancers bear out Tacitus’ tale of naked youths dancing with weapons in hand. Naked, the youths were berserks. Assyrian berserks, Celtic Gaesati, even Aztec wild warriors all danced naked. Indeed, being barefooted and barechested as the best getup for strenuous dancing may, in itself, have been a reason for fighting naked. Woden, as god of the berserks, led the dance. A Danish bracteate gold amulet shows him dancing, wearing but a helmet, a neckband, and a hitherto overlooked belt-like the warriors from Grevenswaenge, Hirschlanden, and elsewhere. Overarmed, like a hero, he twirls shield, ax, spear, and club, all bent to show that he shakes them as he dances (see the pic.).

Rhythmic song and dance bonded the warriors together, entranced them, and aroused their fighting madness. War dances, like war songs, however, also re-enacted mythical battles and thereby changed warriors into mythic heroes. As Mircea Eliade has put it, “The frenzied berserkir ferocious warriors realized precisely the state of the sacred fury (wut, menos, furor) of the primordial world.”

Woden’s wolf tail, recognizable on the Danish medallion by its bent-up tip, makes him also a wolf-warrior and shape-shifter. Changing into animal shapes, as it were, had much in common with being overcome by battle madness; this may be how bear- and wolf­ warriors, too, came to be seen as wild and woundproof, in a word, berserk.

Whether all ancient naked or half-naked warriors thought themselves woundproof, as did their medieval counterparts, is an open question. The psychological and physiological state of fighting frenzy with its rise of adrenaline levels could foster such a belief, for adrenaline “dilates the airways to improve breathing and narrows blood vessels in the skin and intestine so that an increased flow of blood reaches the muscles, allowing them to cope with the demands of the exercise… . During surgery, it is injected into tissues to reduce bleeding.”

Buoyed by this “adrenaline rush,” frenzied fighters may well have thought themselves stronger and less vulnerable than others. Vergil says of the Latin Messapus that neither fire nor steel hurt him. Of some Italic wolf-warriors such as the Hirpi Sarani, it was said that they too were not hurt by fire. These are but scattered and vague hints for antiquity. We are on firmer ground in the Nordic middle ages. In the latter period, berserks, as followers of Woden, thought themselves safe from wounds by iron and fire, vulnerable only to wooden clubs. Half-way around the world, the Malabar amoks, … "stopped neither at fire nor sword.“

Whether all half-naked warriors of antiquity roused themselves to fighting madness is unknown. It is likely, though, for Strabo says that all Celts and Germans were battle-mad, and if regular warriors were prone to battle madness, elite warriors in the first line would have raged even more. Battlefield madness was certainly a telling trait of many Indo-European warriors, for they craved the fame and "unwilting glory” praised in the Iliad and in the Rig Veda alike.

To linguists, words and concepts shared by Indo-Europeans suggest that fighting madly was a very old custom that originated perhaps in the fourth millennium B.C. The word for “mad attack,” eis-, shared by Vedic, Iranian, and Germanic warriors, makes it likely that the berserk fighting style comes from the time before the dispersal of the lndo-­Europeans. Dumezil put it thus:

Aesma [to Zoroastrians] is one of the worst evils, and later, in the eyes of the Mazdaeans, the most frightful demon, who bodies forth the destructive fury of society. Yet it only personifies as something bad a quality that gives the Rig Veda, from the same root, an adjective of praise for the Maruts, the followers of Indra, and for their father, the dreadful Rudra: ismin “impetuous” and no doubt “furious.” These words come from the root of Greek οίστρος, Latin ira, and, it seems, from the Old Norse verb eiskra that describes the rage of the wild berserk warriors; hence we meet here a technical term of the Indo-European “warrior bands.”

The mind of berserk warriors in the second millennium B.C. was much the same, it seems, as that of medieval warriors two thousand years later. In English, the word “mind,” related to “mania,” comes from the same root as the Sanskrit manas and Greek menos, both meaning “spirit” as well as “fury.” For Homeric warriors menos meant “a temporary urge of one, many, or all bodily or mental organs to do something specific, an urge one can see but not influence.” Menos came from above; heroes owed their great deeds to it, and Indo-European heroic poetry sings its praise.  From it arose sundry forms of abandoning oneself to new identities such as those of wolf-warriors and berserks.

In Old Norse the word berserk at first meant a bear-shirt warrior. But when bera (bear) became bjom, the word berserk was no longer understood as bear-warrior and instead came to mean “bare-shirt.” Since those who fought without shirt and armor were reckless mad­ men, the word berserk took on its modem meaning of mad fighter. The old bear-warrior meaning is still seen, however, in the berserk custom of “biting” one’s shield. The custom is known from Snorri Sturlusson's Ynglinga saga, quoted above, but also from the famous twelfth­century chess set found on the Isle of Lewis in the Outer Hebrides. Some of the warrior pawns in that set “bite” their shields. Biting rapidly on a shield makes a sound like that of bears clacking their teeth just before they attack. Shield-biting that sounded like threatening bears further deepened the warrior’s shape-shifting trance.

Berserks thus embody an abiding spirit in unbroken tradition from Vedic and Homeric times to those of the Icelandic sagas. The history of berserk warriors offers rich religious, cultural, and military detail from about 1300 B.C. to A.D. 1300 and links the bronze, iron, and middle ages, three thousand years of history seldom understood as belonging together.”

~ Michael P. Speidel, Berserks: A History of Indo-European “Mad Warriors”