A series of about 5,200 boreholes stretching nearly a mile (1.5 kilometers) across the Pisco Valley in the southern Peruvian Andes has baffled researchers for nearly a century. But a new look at the site, called Monte Sierpe, or “serpent mountain,” may help archaeologists decipher why the ancients built it hundreds of years ago.
The “band of holes,” as it is informally called, first garnered attention when National Geographic published aerial photographs of the site in 1933.
But there are no written records relating to the formation, leaving its purpose open to interpretation – and there were many. Hypotheses about the use of the holes included defense, accounting, storage, gardening, water collection, and fog capture purposes. People who support the theory of ancient astronauts, a belief that aliens are real and formed early civilizations on Earth, have also suggested extraterrestrial connections.
Now, new drone footage and microbotanical analysis of pollen grains found in the holes are leading researchers to suggest that the site first served as a bustling market for a pre-Inca civilization, and later as an accounting method for the Incas, according to a study published Nov. 10 in the journal Antiquity.
“Why did the ancient peoples make more than 5,000 holes in the hills of southern Peru?” said the lead author of the study Dr. Jacob Bongers, digital archaeologist at the University of Sydney and Visiting Research Fellow at the Australian Museum Research Institute. “We don’t know why we’re here, but we’ve produced some promising new data that provide important clues and support new theories about the site’s use.”
A look back in time
The sheer scale of Monte Sierpe made it difficult to study, but drone technology allowed a new perspective, said study coauthor Charles Stanish, a professor in the department of anthropology at the University of South Florida.
Each hole has a width of 3.3 to 6.6 feet (1 to 2 meters) and a depth of 1.6 to 3.3 feet (0.5 to 1 meter). Drone photography shows they are organized into about 60 distinct sections that are separated by empty spaces, Bongers said. His team was also able to identify patterns – for example, a section of 12 rows alternating between seven and eight holes, suggesting that the organization is not random, he added.
Crops and other objects may have been placed in the holes hundreds of years ago. – C. Stanish
Ancient pollen grains found inside the holes indicate the presence of crops such as corn, as well as wild plants including reeds and willows that were traditionally used to make baskets, Bongers noted.
Crops and other objects may have been placed in these baskets or deposited in the holes, which may have been covered with plant material. It is possible that structures were also built on or near the holes, Bongers said, but there is no evidence left if any architecture ever existed.
The team believes that the indigenous people of the pre-Inca Chincha Kingdom from the coast and hills of Peru may have come to exchange goods and barter using their own goods, rather than currency.
“Perhaps other important resources like cotton, coca, corn, and chili peppers were put in the holes and exchanged,” said Bongers. “For example, a certain number of holes containing maize would have been equivalent to a certain number of holes containing another type of object, such as cotton or coca.”
The clear evidence provided by the pollen helps rule out many of the other proposed uses of the site, said Dr. Dennis Ogburn, an associate professor in the department of anthropology at the University of North Carolina at Charlotte. Ogburn did not participate in the new study.
“Monte Sierpe is a site that has truly been a mystery in Andean archaeology, and I am excited to see this research come to fruition,” Ogburn wrote in an email.
Investigate a modified landscape
The dating of the holes suggests that the site was used between 600 and 700 years ago.
While the team is still conducting more radiocarbon dating to determine a precise timeline, they believe it was built during Peru’s Late Intermediate Period, between AD 1000 and 1400, which aligns with the use of the site by the pre-Inca civilization.
Dr. Jacob Bongers used drones to capture high-definition footage of the sprawling site. – J. RodrÃguez
Pollen from citrus plants, introduced to the region during the colonial period between 1531 and 1825, suggests that the site was still in use after the fall of the Inca Empire in 1532 as the Spanish colonized Peru. It was probably eventually abandoned “because the Spanish couldn’t find a way to integrate the site into their economic expansion,” Bongers said.
It is possible that Monte Sierpe included only a few sections of holes as a barter market before it was expanded under the Inca empire.
Or, it may have been completed before the Incas arrived. But either way, the team believes that the Incas used the site as a means of accounting on a large scale.
“In a sense, Monte Sierpe could have been an ‘Excel spreadsheet’ for the Inca Empire,” said Bongers.
The segmented organization of Monte Sierpe reflects an Inca counting system involving knotted cords called khipu. One of these devices, containing 80 groups of cords, was recovered from the Pisco Valley.
“The knotted numbers on these cords show an intricate set of arithmetical interrelationships, suggesting that it is a surviving record” of the accounting operations that may have been used at Monte Sierpe, Bongers said.
Monte Sierpe was ideally positioned for barter and accounting near a pre-Hispanic road network, and between two major Inca sites called Tambo Colorado and Lima La Vieja.
Members of Bongers’ team continue to study the khipus from Peru to test any potential numerical relationships between the Monte Sierpe design and the Inca numbering system. If there is a connection, the holes may have been how the empire collected tribute, an early form of taxes, from local communities.
Because the market and accounting systems operated in two very different ways, and that the connection between the holes and Inca khipus is weak, more support is needed to be convincing, said Ogburn.
The preservation of the ancient heritage
As new research aims to uncover the secrets of Monte Sierpe, future findings may shed light on a piece of history that has not been well preserved.
“The Andes is one of the few regions of the world where ancient and large-scale societies developed, such as the Inca Empire, but there is no strong evidence for pre-Hispanic coins or writing systems,” said Bongers.
The “band of holes” was ideally situated in the Pisco Valley to bring people together, Bongers said. – JL Bongers
Dr. Christian Mader, leader of the research group at the Center for Dependency and Slavery Studies of the University of Bonn in Germany, believes that the document is an important contribution to Andean archaeology, as well as the study of ancient economies. While Mader did not participate in this research, his work focused on pre-Hispanic economies and exchange.
“Their proposal that the site served as a market during the Late Intermediate period and as a means of accounting for goods and tribute under the Inca Empire is interesting and compelling,” Mader wrote in an email. “And this paper shows how much we still have to learn about Indigenous economic mechanisms.”
Monte Sierpe presents a puzzle that is difficult to interpret, Bongers said, and part of the puzzle is presenting hypotheses, rather than arguments, that can be further tested to better understand the local heritage.
“The narratives we build about local cultural heritage have a real impact,” said Bongers. “It is crucial to ensure that such narratives incorporate Indigenous perspectives and archaeological evidence to accurately represent local heritage.”
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