More than 20 years ago, Dr. Heiko Prümers of the German Archaeological Institute and Professor Dr. Carla Jaimes Betancourt of the University of Bonn, then a student in La Paz, began archaeological excavations on two “mounds” near from the village of Casarabe in Bolivia. The Mojos Plains are a southwestern fringe of the Amazon region. Even if the savannah plain, flooded several months a year during the rainy season, does not favor permanent settlement, there are still many visible traces of the period preceding Spanish colonization at the beginning of the 16th century. Apart from the “mounds”, these traces mainly include causeways and canals that often lead for miles in a straight line through the savannahs.
“This indicated a relatively dense settlement in pre-Hispanic times. Our goal was to carry out basic research and trace the settlements and life there,” says Heiko Prümers. In previous studies, researchers have already found that the Casarabe culture – named after the nearby village – dates back to the period between 500 and 1400 AD and, according to current knowledge, extended over an area of approximately 16,000 square kilometers. eroded pyramidal stumps and platform buildings.
Initial conventional surveys revealed a central terraced area, a ditch wall surrounding the site and channels. Moreover, it became apparent that some of these pre-Hispanic settlements were enormous in size. “However, the dense vegetation under which these colonies were located prevented us from seeing the structural details of the monumental mounds and their surroundings,” explains Carla Jaimes Betancourt of the Department of Anthropology of the Americas at the University of Bonn.
LIDAR technology used for the first time in the Amazon
To find out more, the researchers used airborne LIDAR (Light Detection and Ranging) laser technology for the first time in the Amazon region. This involves surveying the terrain with a laser scanner attached to a helicopter, small plane or drone that transmits around 1.5 million laser pulses per second. In a subsequent evaluation step, the vegetation is digitally removed, creating a digital model of the land surface, which can also be displayed as a 3D image. “The first results were excellent and showed how effective the technology was even in dense tropical forest. From that moment, the desire arose to map the large colonies of the Casarabe culture using LIDAR technology,” explains Dr. Heiko Prümers, head of the study.
For the current study, in 2019 the team with Professor José Iriarte and Mark Robinson from the University of Exeter, mapped a total of 200 square kilometers of the Casarabe cultural area. The evaluation made by the company ArcTron3 reserved a surprise. What emerged were two remarkably large sites of 147 hectares and 315 hectares in a dense four-tier settlement system. “With a north-south extension of 1.5 kilometers and an east-west extension of around one kilometer, the largest site discovered to date is as large as Bonn in the 17th century,” says co-author Prof. Carla Jaimes Betancourt. .
It is not yet possible to estimate how many people lived there. “However, the layout of the settlement itself tells us that planners and many active hands were at work here,” says Heiko Prümers. Changes to the settlement, for example the expansion of the rampart-moat system, also show a reasonable increase in population. “For the first time, we can refer to pre-Hispanic urban planning in the Amazon and show the map of the site of Cotoca, the largest settlement of the Casarabe culture that we know of to date,” Prümers points out. In other parts of the world, similar agrarian towns with low population density had already been found.
LIDAR shows human-altered landscape
The LIDAR cartography reveals the architecture of the large squares of the village. Stepped platforms topped with U-shaped structures, mounds of rectangular platforms and conical pyramids (up to 22 meters high). Causeway-like paths and canals connect individual settlements and indicate a tight social fabric. At least one other colony can be found within five kilometers of each of the colonies known today. “So the whole area was densely populated, a pattern that overturns all previous ideas,” says Carla James Betancourt, a member of the transdisciplinary research area “Present Pasts” at the University of Bonn.
The researchers point out that despite all the euphoria generated by the site maps and the possibilities they offer to reinterpret the settlements in their geographical setting, the real archaeological work has only just begun. The goal for the future, they say, is to understand how these large regional centers work.
“Time is running out as the spread of mechanical agriculture is destroying a pre-Columbian structure in the Llanos de Mojos region every month, including mounds, canals and causeways,” Betancourt says. With that in mind, says Betancourt, Lidar is not just a tool for documenting archaeological sites, but also for planning and preserving the impressive cultural heritage of indigenous peoples in the Amazon.