The first European contact with the Amazon river took place in the
mid-16th century: Orellana navigated the whole length of the river in
1541 and so did the dramatic expedition of Pedro de Urzua and Lope de Aguirre 20 years later. The chronicles of the two expeditions, as well as later documentation, attest to the presence of a number of villages and of numerous «nations» along the banks of the river (the so called várzea). Two centuries later, the river was depopulated because of slaving expeditions, conflicts and wars, the Portuguese-Spanish rivalry, dislocation and dispersion in the interior, and high mortality induced by new diseases. Although the numerical evidence is thin - and limited to the enumerations carried out by the Jesuits in the missions in the upper Amazon - the ethnological/anthropological one is rich. The paper is an account of the disaster that brought down the population from a few million at contact to a few hundred thousand at the beginning of the 19th century.