Researchers from the University of Sydney have proposed that the ancient Monte Sierpe site in Peru's Pisco Valley, known as the Band of Holes, served as a pre-Inca marketplace before being repurposed by the Inca Empire for accounting. Using drone mapping and soil analysis, the team uncovered evidence of trade and numerical patterns resembling Inca khipu devices. The findings, published on November 10, 2025, in Antiquity, suggest the site facilitated barter and tribute collection.
In southern Peru's Pisco Valley, the Monte Sierpe site—often called the Band of Holes—consists of roughly 5,200 uniform holes, each 1-2 meters wide and 0.5-1 meter deep, arranged in rows over 1.5 kilometers. First documented in 1933 through aerial photos in National Geographic, the site's purpose has long eluded archaeologists, with past hypotheses including defense, storage, water collection, and gardening.
Dr. Jacob Bongers, a digital archaeologist at the University of Sydney and lead author, led an international team that employed high-resolution drone imagery and microbotanical analysis of soil samples from the holes. The drones revealed numerical patterns in the layout, mirroring the structure of an Inca khipu, a knotted-string recording device found in the same valley. Soil traces included maize, an essential Andean crop, and reeds used for weaving baskets, indicating plant materials were placed in the holes, possibly in woven containers for transport.
"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," said Dr. Bongers.
The site's location between two Inca administrative centers and near pre-Hispanic road crossroads in the chaupiyunga ecological zone supports its role as a trade hub. Evidence points to the pre-Inca Chincha Kingdom building it for organized barter among traders, farmers, and fisherfolk in a population of around 100,000. Under Inca rule, it evolved into an accounting system for managing resources and tribute.
"Perhaps this was a pre-Inca marketplace, like a flea market... 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," Dr. Bongers explained.
Professor Charles Stanish, senior co-author from the University of South Florida, noted the site's prior lack of study due to isolation and haze, but drone technology enabled precise mapping. "This is a spectacular find," he said, emphasizing how it debunks pseudoarchaeological claims and highlights Indigenous practices.
The research, supported by grants from the Franklin Research Grant and others, was permitted by Peru's Ministry of Culture.