Iconic Andean monument may have been used for Indigenous accounting

Sediment analysis and drone photography of the iconic South American site Monte Sierpe (also known as the Hole Strip) support a new interpretation of this enigmatic landscape feature as part of an indigenous system of record and exchange.

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

It first attracted modern attention in 1933, when a magazine published aerial photographs of the holes. National Geographicbut the purpose of the monument is still unclear.

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

To shed new light on this controversial feature of Peru's ancient landscape, an international team combined microbotanical analysis of sediment samples from the pits with high-resolution aerial photographs, providing new insight into the organization and use of Monte Sierpe at both the micro and macro levels. Their results published in the magazine Antiquity.

According to the authors, their most important discovery is microbotanical data showing that the pits contain remains of plants, including crops such as corn and wild plants which are traditionally used to make baskets.

“These findings support the hypothesis that in pre-Hispanic times, local groups periodically lined pits with plant materials and stored goods in them, using wicker baskets and/or bundles for transport,” explains Dr Bongers.

However, perhaps most intriguing is aerial photographswhich indicates numerical patterns in the arrangement of holes. Combined with the segmented organization of the site, Monte Sierpe reflects the quipu: Incan counting devices made from knotted rope.

This could indicate that Monte Sierpe was a monumental accounting system during the Inca period, administered by the Inca state to collect tribute.

It is important to note that Monte Sierpe is strategically located between two Inca administrative sites and near the intersection of a pre-Hispanic road network. It is located in a transitional ecological zone (chaupiunga) between the highlands and the lower coastal plain, an area where groups from both regions met and exchanged goods.

Combined with microbotanical and aerial photography, this suggests that Monte Sierpe was originally built and used by the pre-Inca kingdom of Chincha for regulated barter and exchange, and later developed into a place of accounting under Inca rule.

“This study provides an important example from the Andean region of how past communities reshaped past landscapes to bring people together and promote interaction,” Dr. Bongers concludes. “Our results expand our understanding of barter markets and the origins and diversity of indigenous accounting practices in the ancient Andes and beyond.”