A petroglyph is an image created by removing part of a rock surface by incising, picking, carving, or abrading, as a form of rock art. The term generally refers to rock engravings of ancient origin, often associated with prehistoric peoples. The oldest petroglyphs in the world are deemed to be those at Murujuga in Western Australia, which are 40–50,000 years old. Some petroglyphs are classified as protected monuments and some have been added to the list of UNESCO's World Heritage Sites, or such status has been applied for.