A mountain-sized mystery
In the arid Pisco Valley of southern Peru, a peculiar feature marks the terrain. Known as Monte Sierpe, or "Serpent Mountain," a band of approximately 5,200 holes stretches for 1.5 kilometers over the uneven terrain. First brought to wide attention by aerial photographs in a 1933 issue of National Geographic, the site has puzzled researchers for nearly a century. The individual pits measure between 1 and 2 meters wide and 0.5 to 1 meter deep. They are not randomly scattered but arranged in distinct blocks and organized rows, forming a pattern that is only truly comprehensible from the air.
Initial theories about their purpose were varied. Suggestions included defensive positions, burial sites, or large-scale storage for food or water. None of these hypotheses held up to scrutiny. The pits are too shallow for effective defense or long-term storage, and no human remains have ever been found within them. The mystery deepened as the sheer scale of the construction became clear. A team of 100 workers could have constructed the entire feature in a month, a significant but manageable feat for an organized state.
From marketplace to tax ledger
Recent archaeological work, led by researchers like Jacob Bongers and Charles Stanish, has offered a new explanation. By using drones to create high-resolution maps and analyzing sediment from within the pits, they uncovered two main phases of use. Radiocarbon dating and pottery styles suggest the holes were first created during the Late Intermediate Period (around 1000–1400 CE), when the Chincha Kingdom controlled the region. During this time, Monte Sierpe likely functioned as a large-scale barter marketplace. The site sits at a strategic crossroads of pre-Hispanic roads, an ideal meeting point for traders from the coast and the highlands. Microbotanical analysis of soil samples revealed traces of maize and reeds, evidence that people placed goods into the holes, possibly using woven baskets. The pits could have served as standardized units of measure, allowing traders to visually assess quantities and negotiate fair exchanges of goods like cotton or chili peppers.
Later, around the 15th century, the Inca Empire expanded and absorbed the Chincha Kingdom. The Inca likely repurposed the existing infrastructure of Monte Sierpe for their own state-run economy. The organized, segmented layout of the holes looks similar to Inca khipus, complex knotted-string devices used for accounting and record-keeping. Researchers propose that the Band of Holes became a monumental accounting device, a physical ledger carved into the earth. Each segment of holes may have corresponded to a specific kin group or village responsible for paying tribute to the Inca state.