Iconic Andean monument may have been used for Indigenous accounting

Sediment analysis and drone photography of the iconic South American monument of Monte Sierpe (aka “Band of Holes”) support a new interpretation of this mysterious landscape feature as part of an Indigenous system of accounting and exchange.

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

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

“Hypotheses regarding Monte Sierpe’s purpose range from defense, storage, and accounting to water collection, fog capture, and gardening,” says lead author Dr. Jacob Bongers from the University of Sydney. “The function of the site remains unclear.”

To shed new light on this ambiguous feature of Peru’s ancient landscape, an international team combined microbotanical analysis of sediment samples from the holes with high-resolution aerial imagery, presenting new insights into Monte Sierpe’s organization and use at both micro and macro scales. Their results are published in the journal Antiquity.

According to the authors, their most important finding is the microbotanical evidence, which uncovered plant remains in the holes including crops such as maize and wild plants that are traditionally used for making baskets.

“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,” explains Dr. Bongers.

Perhaps most intriguing, however, is the aerial imagery, which indicates numerical patterns in the layout of the holes. Combined with the monument’s segmented organization, Monte Sierpe mirrors khipus: Inca counting devices made from knotted string.

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.

Importantly, Monte Sierpe is strategically located between two Inca administrative sites and near the intersection of a network of pre-Hispanic roads. It is positioned in a transitional ecological zone (chaupiyunga) between the highlands and lower coastal plain, a space where groups from both regions would have met and exchanged goods.

Combined with the microbotanical and aerial findings, this suggests that Monte Sierpe was initially constructed and used by the pre-Inca Chincha Kingdom for regulated barter and exchange, later developing into an accounting place under Inca rule.

“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.”