Some months later, only half of the 4,000 Spaniards and their indigenous guides remained. Pizarro’s expedition had ground to a halt at the edge of the rainforest — a point no European had ever reached. All food was gone, turning back was impossible, and the hunger for gold had given way to the will to survive. In despair, the Spaniards decided to build a caravel on the Coca River, deep in the rainforest, to continue their journey by water.

While Pizarro lay in feverish delirium, the young, aristocratic and resourceful Francisco de Orellana took control, setting off with 61 others to find help. But the vessel Victoria would never make it back to base camp. It was swept into an extraordinary journey down the Amazon. The expedition’s priest, Gaspar de Carvajal, wrote in his diary of headhunters and fearsome naked female warriors — the Amazons.

In 2003, Dutch naturalist Dr. Marc van Roosmalen sailed the research vessel Calibella along the Rio Aripuanã, one of the countless tributaries of the Amazon. TIME magazine had named Roosmalen one of its “Heroes of the Planet.” Over the previous twenty years, the primatologist had discovered more than twenty new animal species — and this had brought him into serious conflict with the Brazilian authorities. Marc van Roosmalen is an official scientist at the prestigious research institute INPA. But the police harass him at every opportunity, because he is attempting to purchase large areas of rainforest with European donations and turn them into protected areas. This is not the best way to make friends in one of the most corrupt countries in South America.