For nearly a century, the enigmatic Monte Sierpe monument in Peru has puzzled archaeologists with its thousands of mysterious aligned holes, with many theories being put forward for their purpose. With ideas ranging from systems to collect water or even an Inca tax, standing burials, grain storage, defense, trail marking, to a sophisticated agricultural system. New research combining microbotanical analysis and aerial photography suggests this iconic Andean feature served first as a sophisticated marketplace and later as an accounting system, revealing evidence of Indigenous economic practices long before European contact. Could this theory finally have found the answer to Peru’s baffling Band of Holes?

Stretching for around a mile (1.5 km) across the rugged terrain of the Pisco Valley in southern Peru, Monte Sierpe—meaning "serpent mountain"—consists of approximately 5,200 precisely aligned holes, each measuring 1-2 meters wide and 0.5-1 meter deep. The monument's holes are organized into distinct sections or blocks, creating a pattern that has confounded researchers since it first gained modern attention through aerial photographs published in National Geographic in 1933.

From Marketplace to Monument: Uncovering Monte Sierpe's Purpose

Dr. Jacob Bongers from the University of Sydney led an international team that has published their findings in the journal Antiquity, presenting what may be the most compelling explanation yet for this landscape feature. "Hypotheses regarding Monte Sierpe's purpose range from defense, storage, and accounting to water collection, fog capture, and gardening," explains Dr. Bongers."The function of the site remains unclear."

The research team's microbotanical analysis of sediment samples from the holes revealed plant remains including maize and wild plants traditionally used for basket-making.

"These data support the hypothesis that during pre-Hispanic times, local groups periodically lined the holes with plant materials and deposited goods inside them, using woven baskets and/or bundles for transport," Dr. Bongers notes.

This discovery provides the first direct physical evidence of how the monument was actually used, moving beyond speculation to concrete archaeological data, and adding to the evidence fro similar theories that have been provided, for example by Stanish and Tantalean in 2015.

Individual holes at Monte Sierpe demonstrate remarkable precision and uniformity. (C. Stanish/Antiquity Publications Ltd)

The Khipu Connection: Reading Landscape as Language

Perhaps the most intriguing finding comes from high-resolution aerial imagery, which reveals numerical patterns in the layout of the holes. Combined with the monument's segmented organization, Monte Sierpe mirrors khipus—the Inca counting devices made from knotted strings used throughout the empire for record-keeping and administration.

This could indicate that Monte Sierpe constituted a monumental system of accounting during the Inca period, administered by the Inca state for the collection of tributes from local populations. The strategic positioning of the site supports this interpretation—Monte Sierpe sits between two Inca administrative sites and near the intersection of a network of pre-Hispanic roads.

Khipu found near Pisco now held in the Ethnologisches Museum, Berlin: top) VA 16135a; bottom) VA 16135b (© Ethnologisches Museum, Staatliche Museen zu Berlin, photographs by Claudia Obrocki. (CC BY-NC-SA 4.0/Antiquity Publications Ltd)

A Meeting Place Between Worlds

The monument's location in a transitional ecological zone called chaupiyunga—between the highlands and lower coastal plain—provides crucial context for trying to unravel its original purpose. This positioning would have made it an ideal space where groups from both regions could meet and exchange goods, operating as a regulated barter marketplace.

The evidence suggests that Monte Sierpe was initially constructed and used by the pre-Inca Chincha Kingdom for regulated barter and exchange. Under later Inca rule, the site evolved into an accounting place where the state could systematically gather tribute from local communities, integrating Indigenous economic practices into the imperial administrative system.

Expanding Our Understanding of Indigenous Innovation

"This study contributes an important Andean case study on how past communities modified past landscapes to bring people together and promote interaction," Dr. Bongers concludes.

"Our findings expand our understanding of barter marketplaces and the origins and diversity of Indigenous accounting practices within and beyond the ancient Andes."

The research demonstrates how pre-Columbian societies developed sophisticated systems for economic administration and social organization that were uniquely adapted to their environmental and cultural contexts. Rather than simply imposing their own systems, the Inca often incorporated and built upon existing Indigenous practices—a strategy that contributed to their successful expansion across such diverse territories.

This thorough and revealing research at Monte Sierpe adds to our growing appreciation of the complexity and innovation of pre-Columbian American civilizations. It reveals how ancient peoples perhaps created monumental expressions of economic and social systems, literally writing their accounting practices into the landscape itself. The monument stands as a testament to the ingenuity of Indigenous accounting methods that served complex societies for centuries without written language as we typically understand it.