Pre-Columbian populations (prior to the arrival of Europeans in the Americas in the 1490s) extended across southern Amazonia, suggests a study published in Nature Communications this week. The study reports newly discovered earthworks, including fortified villages, dating to 1250-1500 AD in the Upper Tapajos Basin. The results suggest that a 1,800 km stretch of southern Amazonia was occupied by pre-Columbian earth-building cultures.

Jonas Gregorio de Souza and colleagues used satellite images to survey the Upper Tapajos Basin in Brazil, discovering 81 new archaeological sites with a total of 104 earthworks. They then conducted ground surveys of 24 of these sites, finding ceramics, polished stone axes, anthropogenic dark earth (a pre-Columbian type of fertilized soil), and middens (a dump for domestic waste), which confirm that the sites had been inhabited. The sites range from small (approximately 30m diameter) ditched enclosures to large (approximately 400m diameter) hexagonal, fortified settlements with multiple mounds around plazas and sunken roads.

Based on the distribution and size of known earthworks, the authors extrapolate that similar habitations may have extended over more than 400,000 km2 of the southern rim of the Amazon with a population of 500,000 to 1 million people in late pre-Columbian times. Based on their findings, the authors call for a re-evaluation of the role of this region in pre-Columbian cultural developments.