A series of about 5,200 pits 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 fresh look at the site, dubbed Monte Sierpe, or “Snake Mountain,” may help archaeologists understand why ancient people built it hundreds of years ago.
The “Hole Strip,” as it is informally known, first attracted attention when National Geographic published aerial photographs of the site in 1933.
But there is no written record of this formation, leaving its purpose open to interpretation—and there were many. Hypotheses about the pits' uses included protection, accounting, storage, gardening, water collection, and fog capture. People who support the ancient astronaut theory, the belief that aliens are real and formed early civilizations on Earth, also suggest extraterrestrial connections.
Now, new drone footage and microbotanical analysis of pollen grains found in the holes suggest that the site first served as a busy market for the pre-Inca civilization and later as a method of accounting for the Incas, according to a study published Nov. 10 in the journal. Antiquity.
“Why did ancient peoples make more than 5,000 pits in the foothills of southern Peru?” said lead study author Dr Jacob Bongers, a digital archaeologist at the University of Sydney and a visiting fellow at the Australian Museum Research Institute. “We don't know why they are here, but we have some promising new data that provides important clues and supports new theories about the site's use.”
Looking back in time
The sheer size of Monte Sierpe has made it difficult to study, but drone technology has opened a new perspective, said study co-author Charles Stanish, a professor in the anthropology department at the University of South Florida.
Each hole is 3.3 to 6.6 feet (1 to 2 meters) wide and 1.6 to 3.3 feet (0.5 to 1 meter) deep. Drone photos show they are organized into about 60 separate sections separated by empty spaces, Bongers said. His team was also able to identify patterns, such as a patch of 12 rows alternating between seven and eight holes, suggesting the arrangement was not random, he added.
Crops and other goods may have been placed in the pits hundreds of years ago. – K. Stanish
Ancient pollen grains found inside the pits indicate the presence of crops such as corn, as well as wild plants including reeds and willows, which were traditionally used to make baskets, Bongers noted.
Crops and other goods could be placed in these baskets or stored in pits, which could be lined with plant material. It is possible that structures were also built over or near the holes, Bongers said, but there remains no evidence that any architecture ever existed.
The team believes that the indigenous people of the pre-Incan kingdom of Chincha from the coast and highlands of Peru may have arrived to exchange goods and barter, using their own goods rather than currency.
“Perhaps other important resources such as cotton, coca, corn and chili peppers would have been placed in the pits and exchanged,” Bongers said. “For example, a certain number of holes containing corn would be equivalent to a certain number of holes containing another type of commodity, such as cotton or coca.”
The clear evidence provided by the pollen helps rule out many other proposed uses for the site, said Dr. Dennis Ogburn, assistant professor of anthropology at the University of North Carolina at Charlotte. Ogburn was not involved in the new study.
“Monte Sierpe is a site that has truly been a mystery in Andean archeology, and I am very pleased to see this research being done,” Ogburn wrote in an email.
Study of the changed landscape
Dating of the pits suggests that the site was used between 600 and 700 years ago.
Although the team is still doing more radiocarbon dating To determine the exact timeline, they believe it was built during the Late Intermediate Period of Peru, between 1000 and 1400 AD, which would correspond to the use of the site by a pre-Incan civilization.
Dr. Jacob Bongers used drones to capture high-definition footage of the extensive site. – J. Rodriguez
Citrus pollen introduced into 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, when 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 areas of the barter market before it was expanded under the rule of the Inca Empire.
Or perhaps it was completed before the arrival of the Incas. But either way, the team believes the Incas used the site as a large-scale accounting device.
“In a sense, Monte Sierpe could be an Excel spreadsheet for the Inca Empire,” Bongers said.
The segmented organization of Monte Sierpe reflects the Incan counting system, which included tied ropes called quipus. One of these devices, consisting of 80 groups of cords, was discovered in the Pisco Valley.
“The numbers tied on these cords show a complex set of arithmetic relationships, suggesting that this is a surviving record” of accounting transactions that may have been used at Monte Sierpe, Bongers said.
Monte Sierpe was ideally located for exchange and accounting next to a pre-Hispanic road network and between two major Incan settlements called Tambo Colorado and Lima la Vieja.
Members of Bongers' team continue to study the quipa from Peru to test any potential numerical connection between the Monte Sierpe design and the Incan counting system. If there is a connection, the holes could be in the way the empire collected tribute, an early form of tax, from local communities.
Given that the market and accounting systems would operate differently, and the connection between holes and Inca quipus is tenuous, more support is needed to be convincing, Ogburn said.
Preservation of ancient heritage
As new research aims to uncover the secrets of Monte Sierpe, future findings may provide insight into a part of history that has not been well preserved.
“The Andes are one of the few regions in the world where ancient large-scale societies, such as the Inca Empire, developed, but there is no convincing evidence for the existence of pre-Hispanic currencies or writing systems,” Bongers said.
The “strip of holes” is ideally located in the Pisco Valley to bring people together, Bongers said. – J.L. Bongers
Dr Christian Mader, head of the research group at the Center for Dependency and Slavery Research at the University of Bonn in Germany, said the paper was an important contribution to Andean archeology, as well as to the study of ancient economies. Although Mader was not involved in this research, his work focused on pre-Hispanic economics and exchange.
“Their proposal that the site served as a market during the Late Intermediate Period and as a device for recording goods and tribute during the Inca Empire is interesting and compelling,” Mader wrote in an email. “And this paper shows how much we still have to learn about the economic mechanisms of Indigenous peoples.”
According to Bongers, Monte Sierpe presents a puzzle that is difficult to interpret, and part of the puzzle is hypotheses rather than arguments that can be further tested to better understand the local heritage.
“The stories we create about local cultural heritage have a real impact,” Bongers said. “It is critical to ensure that such narratives include Indigenous perspectives and archaeological evidence to accurately represent local heritage.”
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