In archaeology, rock arts are human-made markings placed on natural surfaces, typically vertical stone surfaces. A high proportion of surviving historic and prehistoric rock art is found in caves or partly enclosed rock shelters; this type also may be called cave art or parietal art. A global phenomenon, rock art is found in many culturally diverse regions of the world. It has been produced in many contexts throughout human history. In terms of technique, the four main groups are:cave paintings, petroglyphs, which are carved or scratched into the rock surface, sculpted rock reliefs, and geoglyphs, which are formed on the ground.