“Sometimes there were men called beserkers in a crew [of vikings]. These men would become temporarily insane while in battle. They would throw away their shields and armor, wade into the thick of the enemy, and try to kill everyone. Sometimes while traveling in the boat, a berserker felt a fit of insanity coming on. His friends would put him ashore so he could run wild, smashing trees with his sword or battle-axe until it passed. We do not know for certain what caused these fits, but most likely they resulted from the violent Viking lifestyle.”