Werewolves, also known as lycanthropes, are mythologic humans with the ability to shapeshift into a wolf or wolflike creature, either purposely, by eating Henbane[citation neeed], being bitten by a werewolf or after being placed under a curse. The medieval chronicler Gervase of Tilbury associated the transformation with the appearance of the full moon; however, there is evidence that the association existed among the ancient Greeks, appearing in the writings of Petronius. This concept was rarely associated with the werewolf until the idea was picked up by Gervase. Werewolves have been mentioned in many forms of media, such as the Harry Potter series, and are usually described as vicious monsters.