Monte Sierpe: Thousands of Mysterious ‘Holes’ in Peru May Have Been Ancient Barter Marketplace

Monte Sierpe (translated as “serpent mountain” and known colloquially as the “strip of holes”) is located in the Pisco Valley of southern Peru and consists of approximately 5,200 precisely aligned holes. New research suggests that this archaeological site was originally a barter market, bringing together diverse people for trade and commerce.

Aerial photo of Monte Sierpe, facing northeast. Image credit: Jacob Bongers, University of Sydney.

Stretching 1.5 km across the Pisco Valley in the southern Peruvian Andes, Monte Sierpe is a large row of approximately 5,200 precisely aligned holes (1 to 2 m wide and 0.5 to 1 m deep), organized into sections or blocks.

This remarkable construction probably dates from at least the Late Intermediate Period (CE 1000-1400) and was in continuous use by the Incas (CE 1400-1532).

It first gained attention in 1933, when aerial photographs of the holes were published in National Geographic, but the monument’s purpose is still uncertain.

Hypotheses regarding its purpose range from defense, storage and accounting to water harvesting, fog capture and gardening, but the site’s true function remains unclear.

“Why did ancient people make more than 5,000 holes in the foothills of southern Peru? Were they gardens? Did they capture water? Did they have an agricultural function?” said Dr Jacob Bongers, a digital archaeologist at the University of Sydney.

“We don’t know why they are here, but we have produced promising new data that provide important clues and support new theories about the site’s use.”

Using drone technology, Dr. Bongers and his colleagues mapped the site and found digital patterns in the layout that suggest an underlying intention in the organization of the site.

To their surprise, archaeologists also discovered that the layout of Monte Sierpe is similar to the structure of at least one Inca khipu (an ancient knotted-rope accounting device) found in the same valley.

“This is an extraordinary discovery that expands understanding of the origins and diversity of indigenous accounting practices in the Andes and beyond,” said Dr. Bongers.

Analyzes of the soil from the holes revealed ancient pollens from corn, one of the most important staple crops in the Andes, and reeds traditionally used for millennia to make baskets.

These unexpected findings importantly indicate that people placed plants in the holes, using woven baskets and/or bundles for transport.

“It’s very intriguing. Maybe it was a pre-Inca market, like a flea market,” Dr Bongers said.

“We know that the pre-Hispanic population here was around 100,000 people. Perhaps mobile traders (sea traders and llama caravans), specialists (farmers and fishermen), and others gathered at the site to trade local products such as corn and cotton.”

“Basically, I think of these holes as a kind of social technology that brought people together and later became a large-scale accounting system under the Inca Empire.”

“There are still many other questions: why is this monument only visible here and not everywhere in the Andes?”

“Was Monte Sierpe some sort of ‘khipu landscape’? — but we are getting closer to understanding this mysterious site. It’s very exciting.”

The study was published on November 10, 2025 in the journal Antiquity.

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Jacob L. Bongers and others. Indigenous accounting and trade at Monte Sierpe (“Band of Holes”) in the Pisco Valley, Peru. Antiquitypublished online November 10, 2025; doi: 10.15184/aqy.2025.10237