Petroglyphs of the archaeological site of Las Labradas, situated on the coast of the municipality of San Ignacio (Mexican state of Sinaloa)

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. Outside North America, scholars often use terms such as "carving", "engraving", or other descriptions of the technique to refer to such images. Petroglyphs are found worldwide, and are often associated with prehistoric peoples. The word comes from the Greek prefix petro-, from πέτρα petra meaning "stone", and γλύφω glýphō meaning "carve", and was originally coined in French as pétroglyphe.

Another form of petroglyph, normally found in literate cultures, a rock relief or rock-cut relief is a relief sculpture carved on "living rock" such as a cliff, rather than a detached piece of stone. While these relief carvings are a category of rock art, sometimes found in conjunction with rock-cut architecture,[1] they tend to be omitted in most works on rock art, which concentrate on engravings and paintings by prehistoric or nonliterate cultures. 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.[2] Rock reliefs are generally fairly large, as they need to be to make an impact in the open air. Most have figures that are larger than life-size.

Stylistically, a culture's rock relief carvings relate to other types of sculpture from period concerned. Except for Hittite and Persian examples, they are generally discussed as part of the culture's sculptural practice.[3] The vertical relief is most common, but reliefs on essentially horizontal surfaces are also found. The term relief typically excludes relief carvings inside natural or human-made caves, that are common in India. Natural rock formations made into statues or other sculpture in the round, most famously at the Great Sphinx of Giza, are also usually excluded. Reliefs on large boulders left in their natural location, like the Hittite İmamkullu relief, are likely to be included, but smaller boulders described as stele or carved orthostats.

In scholarly texts, a petroglyph is a rock engraving, whereas a petrograph is a rock painting. In common usage, the two words are synonymous.[4][5][6] Both types of image belong to the wider and more general category of rock art or parietal art. Petroforms, or patterns and shapes made by many large rocks and boulders over the ground, are also quite different. Inuksuit are also not petroglyphs, they are human-made rock forms found only in the Arctic region.

Composite image of petroglyphs from Scandinavia (Häljesta, Västmanland in Sweden). Nordic Bronze Age. The glyphs have been painted to make them more visible.

Petroglyphs have been found in all parts of the globe except Antarctica, with highest concentrations in parts of Africa, Scandinavia, Siberia, southwestern North America, and Australia;[citation needed] many examples of petroglyphs found globally are dated to approximately the Neolithic and late Upper Paleolithic boundary (roughly 10,000 to 12,000 years ago), though some, such as those found at Kamyana Mohyla, were created earlier than this; some petroglyph sites in Australia are estimated to date back 27,000 years, and other examples of petroglyphs are estimated to be as old as 40,000 years.[citation needed]

Around 7,000 to 9,000 years ago, following the introduction of a number of precursors of writing systems, the existence and creation of petroglyphs began to suffer and tail off, with different forms of art, such as pictographs and ideograms, taking their place. However, petroglyphs continued to be created and remained somewhat common, with various cultures continuing to use them for differing lengths of time, including cultures who continued to create them until contact with Western culture was made in the 19th and 20th centuries.[citation needed]

Many hypotheses exist as to the purpose of petroglyphs, depending on their location, age, and subject matter. Some petroglyph images most likely held a deep cultural and religious significance for the societies that created them. Many petroglyphs are thought to represent a type of symbolic or ritualistic language or communication style that remains not fully understood. Others, such as geocontourglyphs, more clearly depict or represent a landform or the surrounding terrain, such as rivers and other geographic features.

Some petroglyph maps, depicting trails, as well as containing symbols communicating the time and distances travelled along those trails, exist; other petroglyph maps act as astronomical markers. As well as holding geographic and astronomical importance, other petroglyphs may also have been a by-product of various rituals: sites in India, for example, have seen some petroglyphs identified as musical instruments or "rock gongs".[7]

Some petroglyphs likely formed types of symbolic communication, such as types of proto-writing. Later glyphs from the Nordic Bronze Age in Scandinavia seem to refer to some form of territorial boundary between tribes, in addition to holding possible religious meanings. Petroglyph styles have been recognised as having local or regional "dialects" from similar or neighboring peoples. Siberian inscriptions loosely resemble an early form of runes, although no direct relationship has been established.

Petroglyphs 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. In 1853, George Tate presented a paper to the Berwick Naturalists' Club, at which a John Collingwood Bruce agreed that the carvings had "... a common origin, and indicate a symbolic meaning, representing some popular thought."[8] In his cataloguing of Scottish rock art, Ronald Morris summarized 104 different theories on their interpretation.[9]

More controversial explanations of similarities are grounded in Jungian psychology and the views of Mircea Eliade. According to these theories it is possible that the similarity of petroglyphs (and other atavistic or archetypal symbols) from different cultures and continents is a result of the genetically inherited structure of the human brain.

Other theories suggest that petroglyphs were carved by spiritual leaders, such as shamans, in an altered state of consciousness,[10] perhaps induced by the use of natural hallucinogens. Many of the geometric patterns (known as form constants) which recur in petroglyphs and cave paintings have been shown by David Lewis-Williams to be hardwired into the human brain. They frequently occur in visual disturbances and hallucinations brought on by drugs, migraine, and other stimuli.

Recent analysis of surveyed and GPS-logged petroglyphs around the world has identified commonalities indicating pre-historic (7,000–3,000 BCE) intense auroras, or natural light display in the sky, observable across the continents.[11][12]

The Rock Art Research Institute (RARI) of the University of the Witwatersrand studies present-day links between religion and rock art among the San people of the Kalahari Desert.[13] Though the San people's artworks are predominantly paintings, the beliefs behind them can perhaps be used as a basis for understanding other types of rock art, including petroglyphs. To quote from the RARI website:

Using knowledge of San beliefs, researchers have shown that the art played a fundamental part in the religious lives of its painters. The art captured things from the San's world behind the rock-face: the other world inhabited by spirit creatures, to which dancers could travel in animal form, and where people of ecstasy could draw power and bring it back for healing, rain-making and capturing the game.[14]

During recent years a large number of rock carvings has been identified in different parts of Iran. The vast majority depict the ibex.[23][24] Rock drawings were found in December 2016 near Golpayegan, Iran, which may be the oldest drawings discovered, with one cluster possibly 40,000 years old. Accurate estimations were unavailable due to US sanctions.[25]

Petroglyphs are the most ancient works of art left by humankind that provide an opening to the past eras of life and help us to discover different aspects of prehistoric lives. Tools to create petroglyphs can be classified by the age and the historical era; they could be flint, thighbone of hunted quarries, or metallic tools. The oldest pictographs in Iran are seen in Yafteh cave in Lorestan that date back 40,000 and the oldest petroglyph discovered belongs to Timareh dating back to 40,800 years ago.

Iran provides demonstrations of script formation from pictogram, ideogram, linear (2300 BC) or proto Elamite, geometric old Elamite script, Pahlevi script, Arabic script (906 years ago), Kufi script, and Farsi script back to at least 250 years ago. More than 50000 petroglyphs have been discovered, extended over all Iran's states.[26]

The oldest reliably dated rock art in the Americas is known as the "Horny Little Man." It is petroglyph depicting a stick figure with an oversized phallus and carved in Lapa do Santo, a cave in central-eastern Brazil and dates from 12,000 to 9,000 years ago.[34]