AI helps uncover hundreds of unknown ancient symbols hidden in Peru’s Nazca Desert

(CNN) — Archaeologists working in Peru, assisted by artificial intelligence, have discovered 303 previously unknown giant symbols carved in the Nazca Desert.

The carvings include birds, plants, spiders, humanlike figures with headdresses, decapitated heads and an orca wielding a knife.

Described in study published Monday in the journal PNAS, the discovery almost doubles the number of known Nazca geoglyphs, mysterious artworks formed in the ground by moving stones or gravel that date back some 2,000 years. The researchers’ findings also shed some light on the symbols’ enigmatic purpose.

Located 50 kilometers (31 miles) inland from Peru’s south coast, the huge symbols were found in the desert beginning in the early 20th century. Some 500 meters (1,640 feet) above sea level, the geoglyphs have survived the ages because the dry desert region is sparsely populated, not affected by flooding and unsuitable for growing crops.

The rate of new finds has increased in recent years due to the use of remote high-resolution imaging, with an average of 19 geoglyphs found annually from 2000 to 2020, according to the research. However, the use of AI to narrow down potential candidates has since turbocharged the pace and, more broadly, promises “a revolution in archaeological discoveries,” according to the study.

A group of researchers led by Masato Sakai, a professor of archaeology at Japan’s Yamagata University, pulled off the latest geoglyph discovery by training an object detection AI model with high-resolution imagery of the 430 Nazca symbols mapped as of 2020. The team included researchers from IBM’s Thomas J. Watson Research Center in Yorktown Heights, New York.

Their main challenge was the limited number of images. Typically, such models are trained with the use of tens of thousands of images, according to the study.

Narrowing the Nazca field

The team chose to focus on the smaller and more figurative of the two types of symbols discovered in the desert. Figurative geoglyphs are typically around 9 meters (30 feet) in length and have been more difficult to identify than the larger line-type, which are 90 meters (98 yards) in length and thus have been more easily spotted during aerial surveys.

The AI model was by no means perfect. It suggested more than 47,000 potential sites from the desert region, which covers 629 square kilometers (243 square miles).

The team screened and ranked those suggestions, identifying 1,309 candidate sites with “high potential.” For every 36 suggestions made by the AI model, the researchers identified “one promising candidate.”

Nonetheless, the study authors noted that the use of AI was a “game changer,” in terms of reducing the amount of labor required to narrow down the search. It allowed the “focus to shift to valuable, targeted fieldwork on the Nazca Pampa,” according to the study.

Between September 2022 and February 2023, the team tested the accuracy of its model in the Nazca Desert, surveying the promising locations by foot and with the use of drones, ultimately “ground truthing” 303 figurative geoglyphs.

“The geoglyphs in good condition were immediately recognized for what they were,” Sakai said in an email. “For those in poor condition, we are investigating what they are through detailed fieldwork.”

Of the 303 newly discovered figurative geoglyphs, 178 were suggested by the model, and 125 were additional finds. Of those, 66 were found as part of an AI-discovered cluster of geoglyphs, while 59 were discovered during the fieldwork without any help from AI.

Many more geoglyphs may be awaiting discovery.

The team was unable to survey 968 of the promising candidates during the fieldwork season detailed in the research. Given the initial success rate of the fieldwork based on the AI model, at least 248 additional figurative geoglyphs could be discovered, according to an estimate from the study.

It is “amazing” to have doubled the number of known geoglyphs, especially given the limited training data, said Amina Jambajantsan, a researcher and data scientist at the Max Planck Institute of Geoanthropology’s Department of Archaeology in Jena, Germany. Jambajantsan wasn’t involved in the Nazca research but uses an AI model to identify burial mounds in Mongolia based on satellite imagery.

Her own work often followed a similar pattern to the Nazca team, she said, with AI-based suggestions often leading to additional discoveries on the ground during fieldwork. “AI is great, but humans are still needed,” she said.

AI has the potential to make huge contributions to archaeology, although the models are not yet perfectly accurate, she said.

“The problem is archaeologists don’t know how to build a machine learning model and data scientists, typically, are not really interested in archaeology because they can get much more money elsewhere,” Jambajantsan added.

Deciphering Nazca symbols’ purpose

It’s not clear why the Nazca people made the symbols. The main hypothesis is that they formed a sacred space that was perhaps a place of pilgrimage. Other theories propose they played a part in calendars, astronomy, irrigation or for movement, such as running or dancing, or communication, the study noted.

An analysis of the newly discovered symbols, along with those already known, revealed some interesting trends, Sakai said.

The larger, line-type geoglyphs easily visible from above typically depict wildlife such as animals or plants, while the smaller, relief-type geoglyphs include humans or things involving humans such as human sacrifice or domesticated llamas.

The survey also more clearly revealed a network of paths in the desert, many of which were close to different groups of symbols.

The smaller geoglyphs were along ancient winding trails likely made throughout the desert by Nazca people viewing the symbols in small groups, according to the study. The bigger Nazca symbols were near networks of straight lines, squares and trapezoids etched into the earth.

These symbols, according to the study, were likely used for ceremonial activities, perhaps at the end of a pilgrimage, and could be regarded as planned, public architecture.

Sakai said work was underway to decipher the precise meaning of the geoglyphs and their mysterious purpose, which the researchers hope to publish in the future.

“Our findings suggest that their meaning is formed through their combinations,” he said, referring to the way the Nazca geoglyphs are grouped together.

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