Hidden in the southern Peruvian Pisco Valley, a mysterious site stretches across the ridges of a hill. Thousands of evenly spaced holes form what locals call Monte Sierpe, or Serpent Mountain or the “Band of Holes.” Viewed from above, the formation resembles the scales of a giant serpent slithering across the landscape. For centuries, the purpose of these holes baffled explorers and archaeologists alike, inspiring theories ranging from religious rituals to extraterrestrial intervention. But recent research is finally unraveling the secret, these holes are part of a sophisticated economic and accounting system used by pre-Inca and Inca societies.
Ever since it was first documented, Monte Sierpe has been shrouded in speculation. Early theories ranged from military fortifications to fog-harvesting systems or ceremonial purposes. “The holes are far too regular and systematic to have been purely ritualistic or defensive,” notes Bruce Bower in his Science News report. The enigmatic site drew the attention of researchers worldwide, who began using drone imagery and sediment analysis to investigate the landscape. Their findings offer a new understanding of what was previously considered a puzzling geological anomaly.
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The Physical Layout of Serpent Mountain
The holes vary in depth from roughly half a meter to one meter and have diameters of one to two meters. They are organized into over 60 distinct blocks, separated by open spaces, with an estimated total of more than 5,200 holes. Some are partially lined with stone, suggesting careful planning and maintenance. The sheer scale and uniformity indicate an administrative function rather than a purely decorative or ritualistic one.
Jacob L. Bongers and colleagues, writing in Antiquity (Cambridge University Press), provide detailed evidence for the economic purpose of the site. Sediment analysis inside the holes revealed remnants of maize and other plants, which were likely traded or used for storage. Radiocarbon dating places the construction of the holes in the Late Intermediate period (AD ~1000–1400), with continued use during the Inca era (AD ~1400–1532).
“Monte Sierpe looks like a snake, and its visual prominence was likely meant to attract trading partners,” Bongers says.
The researchers suggest that the holes functioned as a physical accounting system, similar in concept to the Inca khipu — knotted strings used to record tax, tribute, and other administrative data. Each block of holes may have represented a specific community or kin group required to deliver goods to the Inca state. In this sense, Monte Sierpe was not just a landscape, but an “archive embedded in the earth.”
From Barter Markets to Tribute Collection
Before the Inca expansion, the Pisco Valley was a hub for inter-community trade. Farmers and coastal communities exchanged maize, cotton, seafood, and other products through well-organized barter networks. When the Inca incorporated the region into their empire, the site evolved into a tribute collection and administrative center, with each hole potentially encoding specific information about owed goods, quantities, or contributing households.
This reinterpretation transforms Monte Sierpe from a mysterious formation into a lens through which we can view ancient Andean economic organization. The holes themselves are not mere remnants of past labor but a deliberate system of recording, storing, and regulating production and exchange.
The implications of this discovery extend beyond archaeology. Monte Sierpe demonstrates that human societies have long used landscapes as instruments of communication and record-keeping. The holes were not only functional but also a form of durable, location-based accounting.
Bongers emphasizes the sophistication of this system. “There is no need to invoke aliens or supernatural forces to explain these structures. The evidence shows that humans in this region were capable of highly organized administrative practices.”
Remaining Questions
While the evidence strongly supports an economic and accounting function, many questions remain. How exactly were the holes used to record information? Who monitored them, and how was accuracy ensured? How did this system integrate with the broader Inca tribute network, documented in 16th-century colonial records? Researchers acknowledge that while Monte Sierpe provides crucial insights, further investigation is needed to fully reconstruct its operational mechanics.
For modern readers, Monte Sierpe offers valuable lessons. Creativity in economic organization does not always rely on money or written ledgers; physical landscapes can serve as sophisticated record-keeping tools. The site also highlights the importance of preserving cultural heritage: every mark in the earth holds stories of production, exchange, and governance in ancient societies.
Monte Sierpe, the Band of Holes, is more than a mysterious formation on a Peruvian hill. These thousands of holes, carefully arranged along a ridge, reveal the ingenuity of pre-Inca and Inca civilizations in managing economies, recording tributes, and facilitating trade. What once seemed enigmatic from a distance is now understood as a deliberate, highly organized system — a buried archive that tells a story of human ingenuity, governance, and social organization in the Andes long before written colonial records existed. (Sulung Prasetyo)
