Some of these reliefs exploit the rock's natural properties to define an image.
Rock reliefs have been made in many cultures, especially in the Ancient Near East.
Siberian inscriptions loosely resemble an early form of runes, although no direct relationship has been established. Petrogylphs from different continents show similarities. While people would be inspired by their direct surroundings, it is harder to explain the common styles.
This could be mere coincidence, an indication that certain groups of people migrated widely from some initial common area, or indication of a common origin.
A petroglyph that represents a landform or the surrounding terrain is known as a geocontourglyph.
They might also have been a by-product of other rituals: sites in India, for example, have been identified as musical instruments or "rock gongs".
They frequently occur in visual disturbances and hallucinations brought on by drugs, migraine, and other stimuli.
Around 7,000 to 9,000 years ago, other precursors of writing systems, such as pictographs and ideograms, began to appear.
Petroglyphs were still common though, and some cultures continued using them much longer, even until contact with Western culture was made in the 19th and 20th centuries.
Some petroglyph images probably have deep cultural and religious significance for the societies that created them; in many cases this significance remains for their descendants.
Many petroglyphs are thought to represent some kind of not-yet-fully understood symbolic or ritual language.
Petroglyphs are images created by removing part of a rock surface by incising, picking, carving, or abrading, as a form of rock art.