Archaeologists may have finally solved Peru’s strange “Band of Holes” mystery

• In southern Peru’s Pisco Valley, Monte Sierpe — also known as the “Band of Holes” — features thousands of perfectly aligned circular pits whose true purpose has long puzzled scientists.
• New research combining microbotanical analysis and high-resolution drone imagery offers fresh insight into how and why this mysterious site was built.
• Evidence suggests Monte Sierpe may have first served as a bustling pre-Inca marketplace where traders, farmers, and travelers exchanged goods and ideas.
• Later, under Inca rule, it might have evolved into a sophisticated accounting and tribute system used to manage resources and record exchanges across the empire.

Clues Emerge in the Mystery of Peru’s “Band of Holes”

Researchers from the University of Sydney have found new evidence that could finally explain one of the Andes’ most puzzling archaeological sites. Monte Sierpe (translated as “serpent mountain” and often called the “Band of Holes”) lies in Peru’s Pisco Valley and features more than 5,000 carefully aligned circular depressions carved into the desert hills.

This unusual formation has fascinated and mystified both scientists and the public for decades.

Lead author Dr. Jacob Bongers, a digital archaeologist at the University of Sydney, asked, “Why would ancient peoples make over 5,000 holes in the foothills of southern Peru? Were they gardens? Did they capture water? Did they have an agricultural function? We don’t know why they are here, but we have produced some promising new data that yield important clues and support novel theories about the site’s use.”

Using advanced drone technology, his team mapped the site and found numerical patterns in the layout that suggest deliberate design rather than random placement.

The researchers were astonished to discover that the layout of Monte Sierpe mirrors the structure of an Inca khipu (a knotted-string device used for recording information) found in the same valley.

“This is an extraordinary discovery that expands understandings about the origins and diversity of Indigenous accounting practices within and beyond the Andes,” said Dr. Bongers.

Ancient Plants Reveal Trade and Transport Clues

Soil samples from the holes revealed traces of maize (corn), one of the Andes’ most essential crops, along with reeds that were traditionally used for weaving baskets. These findings show that ancient people placed plant materials into the holes, possibly using woven containers for transport.

“This is very intriguing,” Dr. Bongers said. “Perhaps this was a pre-Inca marketplace, like a flea market. We know the pre-Hispanic population here was around 100,000 people. Perhaps mobile traders (seafaring merchants and llama caravans), specialists (farmers and fisherfolk), and others were coming together at the site to exchange local goods such as corn and cotton. Fundamentally, I view these holes as a type of social technology that brought people together, and later became a large-scale accounting system under the Inca Empire.

“There are still many more questions — why is this monument only seen here and not all over the Andes? Was Monte Sierpe a sort of ‘landscape khipu’? — but we are getting closer to understanding this mysterious site. It is very exciting.”

The team’s findings were published on November 10 in the journal Antiquity.

Stretching for about 1.5 kilometers across the Pisco Valley in southern Peru, Monte Sierpe consists of roughly 5,200 uniform holes, each 1-2 meters wide and 0.5-1 meter deep, arranged in rows and divided into distinct sections.

The site first gained widespread attention in 1933 when aerial photos appeared in National Geographic, but its true purpose has remained uncertain ever since.

“Hypotheses regarding Monte Sierpe’s purpose range from defense, storage, and accounting to water collection, fog capture and gardening, yet the true function of the site remains unclear,” said Dr. Bongers.

Drones and Soil Analysis Offer New Clues

To better understand this enigmatic feature of Peru’s landscape, Dr. Bongers and an international research team combined drone-based aerial photography with microbotanical analysis of sediments collected from the holes. These complementary approaches revealed new details about how the site was organized and used, both at a fine scale and across the broader landscape.

Together, the data support a new interpretation of Monte Sierpe as an Indigenous center for barter and exchange that may have evolved into an accounting system under Inca rule.

Monte Sierpe’s location adds weight to this idea. It sits between two Inca administrative centers and near a crossroads of pre-Hispanic roads. The area occupies a transitional ecological zone (chaupiyunga) between the Andes highlands and the lower coastal plain, an ideal meeting ground for trade between regions.

These findings suggest that the pre-Inca Chincha Kingdom may have built Monte Sierpe for organized barter and trading, and that the Inca later repurposed it for accounting and tribute collection.

“This research contributes an important Andean case study on how past communities modified landscapes to bring people together and promote interaction,” said Dr. Bongers.

International Collaboration and Technological Innovation

Dr. Jacob Bongers specializes in drone-based archaeological mapping and is the Tom Austen Brown Postdoctoral Research Associate in Archaeology at the University of Sydney. He is also a core member of the Vere Gordon Childe Centre (VGCC), which unites experts across disciplines to study humanity through time. In addition, he is a Visiting Research Fellow at the Australian Museum Research Institute.

Professor Kirsten McKenzie, Director of the VGCC, praised his work: “We are all hugely proud of his achievement. Monte Sierpe is a high-profile site that attracts a lot of popular commentary online, including misinformation that threatens to overshadow Indigenous knowledge bases and community ownership over history and heritage.

“Dr. Bongers’ team brought to light an incredible example of Indigenous accounting and exchange through interdisciplinary research and diverse expertise, highlighting how cutting-edge technologies and analyses lead to a completely novel understanding of Andean communities in the past.”

Professor Charles Stanish, senior co-author from the University of South Florida, noted that despite its fame, Monte Sierpe had seen little professional archaeological study since its discovery in the 1930s and limited surveys in the 1970s. “The site is isolated and not threatened by development. As a result, there has not been a sense of urgency,” he explained.

That changed with the advent of drone imaging. “With the recent availability of drone technology, archaeologists detected mathematical patterning in the layout of the holes. This is a spectacular find. Combined with discoveries in the Cañete Valley 75 kilometers north of Inca storage sites with precisely aligned products on the ground in carefully drawn squares, interest in the Band of Holes skyrocketed.”

Professor Stanish added that the site has long drawn public fascination, but reliable data was scarce. “The site has always been very prominent in the pseudoarcheology world with rampant speculation and mischaracterization of the data on the ground. One of the benefits of scientific work is the debunking of unsubstantiated claims that in many ways deprive Indigenous peoples’ rightful ownership of their past.”

Mapping the Andes’ Hidden Patterns

Before drone surveys, it was nearly impossible to grasp the site’s structure from ground level or even from nearby hills because of the persistent coastal haze. “Until drone technology, the site of Monte Sierpe/Band of Holes was extremely difficult to map on the surface. One simply cannot get an accurate impression of the structured nature of the hole segments, even from the top of the mountain behind due to the permanent haze in the area,” said Stanish.

He added, “Furthermore, there were very few artifacts on the ground making it difficult to determine a date for the site. Once we had precision, low-altitude images it was immediately clear that this site was profoundly important and had to be scientifically studied.”

“Now that we have established that this site was for storage and redistribution, our University of South Florida team will conduct additional work to determine the range and origins of the various plants, particularly the medicinal ones,” Professor Stanish said. “With every identification of a new plant type, the Band of Holes becomes more intriguing.”

The research received support from a Franklin Research Grant, the University of South Florida Office of the Dean, and the Cotsen Institute of Archaeology at the University of California, Los Angeles. The team also thanked the Peruvian Ministry of Culture for its research permit (000318-2024-DCIA-DGPA-VMPCIC/MC). Open access funding was provided by the University of Sydney.