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Monte Sierpe (‘Serpent Mountain’), also known as the ‘Band of Holes’, is a curious archaeological feature comprising a 1.5km-long series of thousands of human-made depressions stretching across a ridge in the Pisco Valley, in the southern Peruvian Andes. The holes are, on average, 1-2m wide and 0.5-1m deep, and are precisely aligned and organised into sections.
The site was first photographed in the 1930s and was surveyed in the 1970s, but it has received little attention from professional archaeologists since then. Aerial photos of the site were published in National Geographic in 1933 and attracted considerable public interest. Various theories have been proposed about the possible function of the Band of Holes, including defence, mining, water collection, geoglyph construction, burial, and gardening. Then, around a decade ago, it was suggested that the holes could have functioned as accounting and temporary storage devices; a recent study set out to test this.
The researchers combined high-resolution drone imagery with microbotanical analyses of sediment samples from several holes. The drone imagery identified a total of c.5,200 holes, consistent with earlier estimates, and showed clearly how these are clustered into segmented blocks separated by empty spaces and differentiated by distinct construction styles. Some holes, for example, were lined with stone walls, while others were not. Microbotanical analysis revealed the presence of a range of pollen, phytoliths, and starch grains in the holes. Pollen from pre-Hispanic crops, such as maize, and wild plants, including reeds and willow, were discovered. These findings are consistent with the holes periodically being lined with plant materials and filled with other goods, transported via woven baskets or bundles, in the late pre-Hispanic period. Surface finds of pottery fragments and radiocarbon dating of charcoal from inside one of the holes suggest that Monte Sierpe was constructed during the Late Intermediate period (AD 1000-1400) and saw continued use in the Late Horizon period (AD 1400-1532).
In light of these findings, the researchers propose that Monte Sierpe was created as a barter marketplace by the Chincha Kingdom, a pre-Hispanic polity that controlled the Pisco and neighbouring Chincha valleys during the Late Intermediate Period. Historical records indicate that fairs and markets for exchanging a variety of goods were common in the Andes. However, identifying these barter marketplaces in the archaeological record remains difficult. Such sites were usually located along long-distance trade routes and at the intersection of different ecozones or social groups, as well as near associated residential sites – Monte Sierpe meets all of these criteria.
The site is strategically placed near the intersection of one of the most important pre-Hispanic coast–highland trade routes, as well as several major roads connecting the Chincha and Pisco valleys and the areas beyond. It also sits in the chaupiyunga, a transitional ecological area between the coastal plain and the highland valleys, which was a focal point for interaction between different groups. Finally, a 26ha defensive settlement is known to be located just 1km away from the Band of Holes. When combined with the microbotanical assemblages in the holes, this information supports the idea that local groups may have travelled to the site to exchange goods and socialise. In this scenario, goods would have been deposited in the holes to allow a standardised system of equivalencies typical of barter markets, while the empty areas between sections functioned as ‘crosswalks’ to allow movement across the site.
Meanwhile, they argue, in the Late Horizon period, Monte Sierpe may have played a role in the Inca tribute/accounting system known as mit’a, which required communities to take turns playing labour tax or its equivalent in tribute. The Band of Holes was located between two Inca administrative sites, Tambo Colorado and Lima La Vieja. The authors also found that the layout of Monte Sierpe is similar to an Inca khipu, a knotted-string device used for recording and counting. The site could, therefore, have functioned as an accounting device, with different sections perhaps corresponding to different social groups, who were expected to maintain the holes and deposit goods into these spaces as part of their tribute.
Although these suggestions are only hypotheses at this stage, the study recently published in Antiquity (https://doi.org/10.15184/aqy.2025.10237) offers a new perspective on how past communities may have modified landscapes to bring people together, and lays the foundation for future research at Monte Sierpe.
Text: Amy Brunskill / Images: J L Bongers; C Stanish
