Scholars have long assumed that the Amazon River Basin, which includes the modern countries of Peru, Colombia and Bolivia, only became densely populated after the arrival of Spanish colonizers in the late 15th century. This assumption was based on the simple fact that the land surrounding the basin experiences severe flooding during the rainy seasons, making permanent settlement without the aid of advanced technology virtually impossible.
One of the few skeptics was Heiko Prümers, a Latin American archaeologist who teaches at the University of Bonn. More than 20 years ago, he set out with his colleague Carla Jaimes Betancourt – then a student in La Paz – to investigate two mounds near the village of Casarabe in northern Bolivia. The mounds, a university press release remembers, “turned out to be eroded pyramid stumps and platform buildings”. In other words: proof of payment.
Later studies confirmed Prümers’ suspicions. Bioarchaeological analysis has shown that these buildings were not unoccupied ceremonial sites. Instead, they were used year-round by a community that farmed, fished, and hunted for food. These farmers, named the Casarabe culture, were found throughout northern Bolivia during the Late Holocene era. Their territory was the Llanos de Mojos, a tropical savannah that covers more than 4,500 km2.
Lidar does not lie
Over the years we have learned a lot about the Casarabe culture. We know that they practiced agriculture as well as aquaculture and used water control systems to protect themselves from the Amazon basin. We also know that their society had a surprisingly complex socio-political organization, with trade flowing between the economic bases. They not only built mounds, but also dug canals, ditches and causeways.
This information was gathered from dozens of archaeological sites, many of which were separated by more than 1,000 kilometers. When studying an ancient civilization as dispersed as the Casarabe culture, it can be difficult to visualize how individual settlements relate to each other in three-dimensional space – and this is especially true for such a wild and inaccessible landscape. than the Amazon basin.
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Lacking the logistical resources to cross the Llanos de Mojos on foot, Prümers and Betancourt decided to try to create a map of the Casarabe culture using light detection and ranging technology. This technology, better known as lidar, previously helped archaeologists get a clearer picture of Olmec and Maya town planning in Mesoamerica. Prümers’ team surveyed an area of 204 km2, focusing on the main excavation sites.
Cotoca and Landiva: urban centers
The lidar scans mapped a total of 26 Casarabe colonies, 15 of which were previously known. The researchers then organized the settlements into five distinct categories, based on the dimensions of their architecture, the scale of the water management infrastructure, and the number of causeways leading to and from the sites, among other factors.
Two settlements were considerably larger than the others and probably served as both cultural and economic centers. Named Cotoca and Landíva, they extend over more than 100 hectares and are surrounded by moats and ramparts. “On the Cotoca site”, Prümers research reports“inner defensive structures are only preserved in some sections, which may suggest that as the site developed the ramparts were adapted accordingly.”
Cotoca and Landíva were built around large complexes of civic and ceremonial architecture. Lidar scans revealed that these complexes were built to face north-northwest. This, according to the article, likely reflects a yet unknown cosmological view that may also be present in the uniform orientation of the Casarabe culture burial mounds. Certainly, this practice would be consistent with other pre-Columbian civilizations, notably the Mayas and the Olmecs.
Mapping the Amazon wetlands
Settlements in the second category were significantly smaller, with areas between 21 and 41 hectares. These so-called secondary sites also present a civic-ceremonial architecture built on basic platforms. Settlements belonging to the third and fourth categories are even smaller, covering 2.5 and 0.34 hectares respectively. The fifth category is hypothetical, containing settlements without mounded architecture that could not be detected by lidar.
As expected, the lidar revealed a lot about the urbanism of Casarabe. Most settlements appear to have been built within 10 km of each other. The eastern region of the Llanos de Mojos is significantly denser than the other regions, with the average distance between settlements falling between approximately 1.8 and 4.0 km. Most of the colonies were organized in clusters of 100 to 500 km2 and connected by causeways and canals.
Unsurprisingly, the greatest number of aqueducts are found around Cotoca and Landíva. From Cotoca, in particular, the canals radiate “in all cardinal connections, linking lower-level sites, the Ibare River to the south, and the lakes to the east”. One of these channels, which leads to Laguna San José, is over 7 km long. This impressive feat of engineering highlights the importance of Cotoca, which served as the center of an area of 500 km2.
A new look
More than 20 years after their first investigations, Prümers and Betancourt have challenged everything the academic community thought they knew about pre-Columbian life in the Amazon basin. “At the regional level,” concludes their study, published in May, “lidar data combined with previous archaeological reconnaissance and remote sensing data show that the Casarabe culture has a highly integrated, continuous and dense settlement system.”
The Casarabe culture occupies a special place in the history of archaeological excavations in Latin America. While major pre-Columbian settlements such as Cotoca and Landíva are not unique, the same cannot be said of the many smaller settlements that lidar scans have highlighted. According to Prümers and Betancourt’s study, these places represent “the first known case [of low-density urbanization] for the entire tropical lowlands of South America.
The larger Amazon settlements also compare favorably to other ancient cities in South America. That is to say, they are of a much larger scale than the settlements built along the Andes Mountains as well as the southern Amazon in general. Indeed, the architecture found at both Cotoca and Landíva required perhaps the greatest amount of skilled labor of any construction of the same period on the entire continent.