The Vikings were known throughout Europe as fierce warriors, and no discussion of Viking warrior culture is complete without an examination of the history of berserkers, a particularly wild, violent sect of Norsemen. Berserkers entered a state of animalistic frenzy before combat. This bizarre cult of crazies was eventually outlawed, even in the warrior culture of the Scandinavian Middle Ages, but not before making their mark on history.
If you're interested in Norse berserker history, look no further than this list. Here you will find wild berserker facts and learn about the Viking berserker drugs imbibed before these beastly warriors enter the fray of war. Hold onto your battle-ax because things are about to get kinda berserk.
...a demoniacal frenzy suddenly took him; he furiously bit and devoured the edges of his shield; he kept gulping down fiery coals; he snatched live embers in his mouth and let them pass down into his entrails; he rushed through the perils of crackling fires; and at last, when he had raved through every sort of madness, he turned his sword with raging hand against the hearts of six of his champions. It is doubtful whether this madness came from thirst for battle or natural ferocity.
So to review, this guy entered a state of frenzied rage, ate his own shield, swallowed fire, ran through flames, and, having exhausted all other methods of proving his insanity, took out six champion fighters.
Refusal to retreat from fire and iron is a common theme in berserker mythology. They feared no weapons.
Berserkers did more than intimidate through their lack of armor; they also transformed themselves mentally. Not like, "Oh, I need a more positive state of mind, I'm going to read some Pema Chödrön." Nah, son. Berserkers assumed the mental identity of the predators they sought to emulate.
Literally, the goal of the berserker in battle was to assume the identity and characteristics of a bear or a wolf. And not just imitating, mind you. Berserkers were method actors. In fact, becoming a wolf or bear was the ultimate goal of all the drugs, drinking, and ritual in which the berserkers partook. Living in the woods, emulating these animals served as preparation for the transformation, as did entering a frenzied state.
Men saw that a great bear went before King Hrolf's men, keeping always near the king. He slew more men with his forepaws than any five of the king's champions. Blades and weapons glanced off him, and he brought down both men and horses in King Hjorvard's forces, and everything which came in his path he crushed to death with his teeth, so that panic and terror swept through King Hjorvard's army...
In Norse legend, to "go berserk" was to hamask, which translates as "change form." Those who changed formed by entering berserkergang were considered hamrammr, or "shapestrong."
In some cases, berserkers are described as undergoing drastic physical transformation, though this is no doubt in part hyperbole. Still, in Icelandic tale Egil's Saga, it's written: "the hardest of men, with a touch of uncanny about a number of them...they were built and shaped more like trolls than human beings."
In his Ynglinga saga, Icelandic poet and historian Snorri Sturluson describes the berserkers thus: "His men rushed forward without armour, were as mad as dogs or wolves, bit their shields, and were strong as bears or wild oxen, and killed people at a blow, but neither fire nor iron told upon them. This was called berserkergang."
So, apparently eating shields was just something berserkers did across the board.
Scandinavian kings such as Harald and Halfdan used berserkers as shock troops, or the advance attacking group in a battle. This served two purposes: it cleared the way for the army to follow, and struck fear into the hearts of enemies. Berserkers were also closely associated with the cult of Odin, the god of royalty (among about 100 other things), noted for his association with leadership.
Thus, sending berserkers into combat as the avant-garde may have curried favor with Odin. They were also occasionally used as royal bodyguards.