• New research reveals Peru’s Band of Holes once functioned as a marketplace before becoming Inca accounting infrastructure.
• Drone imaging and microbotanical analyses found maize and reed residues, supporting deliberate pre-Hispanic use for barter and storage.
• Researchers linked the holes’ segmented arrangement to quipu structures, suggesting Inca tribute organization followed hierarchical decimal taxation systems.

Nearly a century ago, the National Geographic Society published a series of mysterious aerial photographs: thousands of neatly aligned indentations that stretched for nearly a mile along a ridge in the foothills of the Peruvian Andes. Ever since, the Band of Holes, as it colloquially became known, has intrigued researchers.

Located on Monte Sierpe (Serpent Mountain) in the coastal desert landscape of southern Peru, it’s a singular form of architectural landscaping that has invited wide-ranging hypotheses regarding its purpose. Over the past four decades, academics have speculated it was used for defense, storage, collecting water, capturing fog, forming geoglyphs, burials, and mining. Proponents of the ancient astronaut theory have also weighed in, offering otherworldly explanations for the more than 5,000 precisely dug holes.

Dispelling the ungrounded theories of these pseudo-archaeologists was one motivation behind a new study that has analyzed the Band of Holes from on high and up close. Led by Jacob Bongers, a digital archaeologist at the University of Sydney, researchers used drone technology to create high-resolution images of the site, microbotanical analysis to look for ancient crop and plant residue, and radiocarbon technology to date the site.

Aerial photograph of Monte Sierpe taken by Robert Shippee and published by the National Geographic Society in 1933. Photo: Bongers et al, Antiquity, courtesy of the American Natural History.

“It is essential to challenge such narratives with clear archaeological evidence and reasoning,” Bongers wrote in a paper published in Antiquity on November 10, 2025. “To ensure that local heritage and Indigenous knowledge are accurately represented in academic and public discourse.”

Bongers’s research suggests the site had two stages of use: first as an indigenous place for barter and exchange, similar to a market; and second as a site used for accounting under Inca rule.

Radiocarbon dating confirms that the site was built between 1000 C.E. and 1400 C.E., a period when the area lay within the Chincha Kingdom, a wealthy and centralized entity that eventually fell under the rule of the Inca Empire. Geography informed function. Located near the intersection of a network of pre-Hispanic roads, Monte Sierpe sits between the highlands and the lower coastal plain, which would have made it a convenient place for people from different groups to gather and exchange goods.

And the peoples of the Chincha Kingdom would have had much to trade. With fertile seas and farmland (they had access to abundant seabird guano) and a population of around 100,000 people, the civilization was extremely productive and would have exchanged its goods for silver, gold, and emeralds with inland traders.

A group of holes at Monte Sierpe. Photo: C. Stantish.

New microbotanical analysis backs up this theory. Sediment samples taken from 19 of the holes, which range from three to six feet in width and two to three feet in depth, found remains of maize and a type of reed that have been used for more than a millennia to make baskets. “The results of our microbotanical analysis support the hypothesis that plants were deliberately placed into the holes during pre-Hispanic times,” the researchers wrote. “Potentially through periodic lining of the holes with plant fibers, or through bundle-making and basketry.”

After the Inca brought the Chincha Kingdom under their rule, the Band of Holes was likely incorporated into the Empire’s system of tribute extraction and accounting. Reviewing images taken by drone, researchers realized the segmented organization of the indentations matched the structure of a quipu, a traditional Andean counting device that uses strings and knots, found nearby in the Pisco Valley at the turn of the 20th century.

Researchers found that the arithmetical relationships between the numbers knotted on the cords of the quipu were similar to those on the ground on Monte Sierpe. Under the Incas, communities were organized into a hierarchical decimal system and expected to pay tribute accordingly. In theory, each section of holes could have corresponded to a specific group for the payment of taxes.

“Our results lay the foundations for future research on Monte Sierpe,” the researchers wrote, “including test excavations, additional radiocarbon dating and sediment analyses, and the study of more local quipu.”