Why did the Inca dig thousands of holes in this mountain? We may now know.
No, it wasn’t built by aliens. But accountants? Maybe.
Along a rocky ridge in Peru, a formation of more than 5,000 closely aligned holes creeps up a mountain like a mile-long snake. When archaeologist Charles Stanish first glimpsed this giant “Band of Holes” more than a decade ago, he'd never seen anything like it. "The site is fascinating," he says.
Also called Monte Sierpe or “Serpent Mountain,” the site has perplexed archaeologists and conspiracy theorists since it was rediscovered during an American expedition to Peru in 1931. A new study from Stanish, now at the University of South Florida, and his colleagues may finally solve the mystery of why this strange formation was built about a thousand years ago.
Based on microbotanical evidence and drone footage, the team argues that the thousands of holes may have been used to measure tributes from groups of local people to their Inca overlords. The analysis, published November 9 in the journal Antiquity, also points to the site’s origins before the Inca Empire’s rise.
Today, Monte Sierpe is remote, in the foothills of the Andes about 20 miles east of the southern Peruvian city of Pisco. But the new work suggest that the Inca appropriated the site because it was once a central place where people came together, to barter for food, cloth, obsidian, and stone tools.
From aliens to Atlantis
Archeologists think that the Band of Holes is about 1,000 years old, and that the local Chincha people came under the control of the Inca Empire about 400 years later. The Chincha lived nearby, but archaeologist do not know exactly who first built the formation.
The site came to modern prominence in 1933, when National Geographic published the first aerial photographs of the unique structure; and Stanish notes it has long been a focus of pseudoarcheological theories, with purported links to ancient astronauts and the myth of Atlantis.
(Were these ancient sites built by aliens? Here’s why some people think so.)
Archaeological studies have suggested a list of much more plausible explanations: It might have been used for defense, for storage, for collecting water, for harvesting fog, or for growing crops.
About 10 years ago, Stanish floated the idea that the Inca used the holes to assess tributes. The new study suggests Band of Holes originated as a barter market and strengthens his original idea with more scientific evidence. (The researchers don't rule out, however, that it may have served only as a ceremonial geoglyph, perhaps like the Nasca lines.)
Telltale traces of an ancient market
In the holes, the team found tiny traces of maize and wild plants traditionally used for making baskets. That suggests people had lined the holes with plant material and deposited goods inside them, while using baskets or bundles to transport the goods, says study lead author Jacob Bongers, an archaeologist at the University of Sydney.
On top of that, the Band of Holes is also located near a nexus of ancient roadways between the coast and the Andean highlands, making it "a good candidate for a barter marketplace," Bongers notes — a logical spot for different groups and specialized merchants to meet and exchange goods.
"Large numbers of people depositing goods in the holes could have been a way of publicly displaying information about the quantity of goods available, as well as the quantity of goods required for a fair exchange," he explains. "For example, a certain number of holes containing maize would have been equivalent to a certain number of holes containing another type of good, such as cotton or coca."
Archaeologist Jordan Dalton of SUNY Oswego likes the idea that Monte Sierpe may have begun as a market. An expert on Inca-era economies, she wasn't involved in the latest study but has worked on sites in the nearby Chincha Valley and visited the Band of Holes. "It's in an important transitory zone between the valleys and the highlands, where different ethnic groups would have come together," she says. "So I think this is a very interesting possibility."
(Satellites spotted 76 strange stone structures in the Andes. What are they?)
A landscape accounting system
As well as the analysis of plant remains in the holes, the researchers used aerial drones to document the Band of Holes from above. They saw that the roughly mile-long structure is composed of more than 60 distinct "blocks" of holes, separated from each other by thin strips of land. Different blocks contain different numbers of rows and numbers of holes in each row.
"One section of the site has at least nine consecutive rows with eight holes each, while another has six consecutive rows with seven holes and one row with eight holes, totaling 50 holes," Bongers says. "Another section has at least 12 rows that alternate between counts of seven and eight."
The details are still unknown, but the researchers think the numerical patterns among the holes at Monte Sierpe may be related to the counting methods used in some khipus—ancient bundles of knotted cords, thought to represent numbers, that are often associated with the Inca but originated with earlier Andean peoples.
(Read more about efforts to decipher Inca string codes.)
In particular, the holes on Monte Sierpe could correspond with the counting method used in one ancient khipu that was found at an archeological site just a few miles away. "In a sense, Monte Sierpe could have been a 'landscape khipu'," Bongers says. The Inca may have appropriated the original marketplace as a way to assess the tributes owed by groups of local people, while reflecting differences in the level of tribute and the number of people who owed that tribute.
If the researchers are correct, the study raises questions about “how past communities modified landscapes to bring people together and promote interaction," Bongers says. Stanish adds that future research will look at the origins of the plant traces found, some of which may have been medicinal. With every discovery, "the Band of Holes becomes more intriguing," he says.
