Werewolves, also known as lycanthropes, are mythological or folkloric humans with the ability to shapeshift into wolves or wolf-like creatures, either purposely, being bitten by another werewolf or after being placed under a curse. This transformation is often associated with the appearance of the full moon, as popularly noted by the medieval chronicler Gervase of Tilbury, although it may have been recognized in earlier times among the ancient Greeks through the writings of Petronius. Werewolves are often granted extra-human strength and senses, far beyond those of both wolves or men. The werewolf is generally held as a European character, although its lore spread through the world in later times. Shape-shifters, similar to werewolves, are common in tales from all over the world, most notably amongst the American Indians, though most of them involve animal forms other than wolves.