In Pliny's Historia Naturalis there is an account of Werewolves, one of the earilest which Pliny himself passes with skepticism.  About a family called Anthus in Arcadia, Greece, one of whose members is chosen by lot every nine years "abrie in deserta transfigurarique in lupum" -  to go away into a deserted place and be transformed into a wolf. 

Around 2,400 years ago, Herodotus wrote about groups of people living in what is now Lithuania and Poland who claimed to turn into wolves for a couple of days a year.