Baring-Gould's eye-opening history of lycanthropy - the werewolf curse - delves deep into the lore, unearthing various historical cases, several of which date back to Ancient or Medieval times.
The concept of a human transforming into a wolf has ancient origins, with several Greek and Roman authors such as Virgil, Ovid, Herodotus and Pliny raising the concept in their poetry and other writings. Rumors of sorcery that could induce a human to change was attributed to magicians in far off places such as Scythia, and such beliefs were widely held.
Later, the Norse civilization's mythology introduced lycanthropy and other kinds of transformation. Humans as wolves, bears, birds and other beasts were said to appear in the northern wilds; the Norse God Odin took the form of a bird on regular occasions. Berserker warriors would clad themselves in wolf skins; Björn, son of Ulfheoin, was famed for his ability to shift between human and wolf forms.
The concept of werewolves only transforming under the full moon seems to have originated later. Baring-Gould notes an early case; a piece of French folklore dating to the late Medieval period, which affirms that certain men are destined to transform under the full moon. The French lore is rich; werewolves are known as louléerou, and certain physiological qualities - such as the shape of the hands and fingers - would remain even in human form.
Sabine Baring-Gould was a priest based in Devonshire, England. Fascinated with old lore, his researches were among the first to organize and present the werewolf folklore, plus many legends and myths of northern Europe. He was immensely interested in the old songs of southeast England, and did much to collect and republish these, that they not fade into obscurity.