Although the Spanish conquistador Francisco de Orellana claimed to have seen indigenous farming villages and huge walled cities along the Rio Negro river in the Amazon basin in 1542, until the last few decades archaeologists doubted the environmentally fragile Amazon flood plain could have provided the resources for cultures to grow beyond small, autonomous villages. However this assumption was disproved when excavations in northeastern Bolivia revealed the existence of an apparently advanced and important civilization, about which we still know very little.

The existence of the Precolumbian Mojos civilization had been known about since the early 20th century, but the region remained little studied up until recently, being overshadowed by more 'glamorous' Andean civilizations like the Inca, the Nazca, and the Tiahuanacans.

The Mojos civilization seems to have been a complex society that developed large urban settlements and intensive farming systems in the Amazon Basin without destroying their environment. Excavations in the Llanos de Mojos flood plain have revealed some 20,000 Mojos settlement mounds ("lomas"), suggesting the area was densely populated. The lomas, which were essentially man-made hills or mounds of pottery sherds mixed with black soil, were surrounded and linked by 5,000 kilometers of artificial earthen causeways, a large network of canals, and 2,000 artificial lakes. The scale of the massive earthworks suggests the Mojos must have possessed a high level of culture and civil engineering skills.

The earthworks appear to have been abandoned between 1400 and 1700 CE, but what caused this important civilization to disappear remains a mystery. A Japanese-Bolivian research team is currently mid-way through a three-year investigation of the Llanos de Mojos mounds, so hopefully will be able to shed further light on both the civilization and the reason for their disappearance.