Archaeologists studying a hillside formation in southern Peru have proposed that thousands of pits carved into the landscape may have functioned as a large scale accounting system used by ancient societies. The site, known as the Band of Holes at Monte Sierpe, contains more than 5,000 carefully arranged pits extending nearly one mile along a ridge in the Pisco Valley.
The unusual formation has puzzled researchers for decades due to its scale and geometric layout. A recent study suggests the pits may have initially supported a system of trade among local communities before later being adapted into a method for recording goods or labor under the expanding administrative systems of the Inca Empire, according to a study published in Antiquity.
The research was led by digital archaeologist Jacob L. Bongers of the University of Sydney, who used drone mapping and microscopic plant analysis to investigate how the site may have been used. The Band of Holes stretches approximately 1.4 kilometers along a hillside and is divided into blocks separated by narrow walkways, suggesting a structured layout that could support organized activity.
Individual pits measure up to two meters in diameter and roughly one meter deep. Researchers observed that pits are arranged in clusters with repeating numerical patterns, including rows with equal counts and alternating sequences. These patterns suggest the layout may have been intentionally designed to track quantities or organize resources.
To investigate how the pits were used, scientists examined microbotanical remains preserved in sediment samples taken from within several pits. These microscopic plant traces included maize pollen along with residues from reeds and bulrush plants commonly used in woven baskets for transporting goods.
The presence of these materials suggests that plant based containers or agricultural products were placed directly into the pits rather than accumulating naturally over time. Researchers interpret this evidence as a possible sign that the pits were used to temporarily store or measure traded goods during exchange events.
The location of Monte Sierpe may also have influenced how the site functioned. The hillside lies within the Chaupiyunga ecological zone, a transitional area between Peru’s coastal plains and Andean highlands. This position would have allowed communities from different regions to meet at a central location to exchange resources such as crops, fish, and manufactured items.
Researchers also identified similarities between the pit arrangements and the logic of Andean record keeping systems known as khipus. Khipus used knotted cords arranged in groups to record numerical information. Some pit clusters display repeating group sizes similar to numerical groupings seen in khipu records discovered in the same valley.
Radiocarbon dating from charcoal recovered within one pit indicates the site was in use around the fourteenth century. This timeframe overlaps with the Late Intermediate Period and the subsequent expansion of the Inca Empire, which implemented administrative systems for managing labor and resources across its territory.
Under Inca governance, communities were often required to contribute labor through the mit’a system, a rotating labor obligation used for agriculture, construction, and state projects. Researchers suggest the Band of Holes could have been adapted to help organize or count goods and contributions during this period.
Alternative explanations for the pits have included theories such as defensive structures, water collection systems, or agricultural installations. However, researchers note that the distribution of plant remains and the consistent numerical patterns in the pit layout appear more consistent with organized storage or counting functions.
Although the accounting interpretation remains tentative, archaeologists say the site provides new insight into how Andean societies may have managed exchange networks and resource distribution using physical landscapes as record keeping systems.
Researchers caution that further excavation and comparative studies are needed to determine whether similar systems existed elsewhere in the Andes.
