Between 1906 and 1914, through a series of expeditions into the Amazon, Fawcett comes to believe that an advanced civilization once existed there. Important clues appear in unexpected places. In 1910, for instance, Fawcett and Costin make contact with a group of supposedly hostile Guarayos who prove friendly. Fawcett notes that the Guarayos have plenty of food and seem to know a great deal about local plants’ medicinal properties. Henceforth, Fawcett appears less interested in mere exploration and increasingly drawn to anthropological and broader scientific pursuits. As a man of his time, he never does transcend the Victorian Era’s obsession with race, but he also develops a genuine regard for the Amazon’s native tribes, as evidenced by his insistence that those tribes’ ancestors were capable of building and sustaining an advanced civilization.

In 1914, Fawcett, Costin, and Manley venture deep into the interior. There, they come upon a clearing, where they discover houses and agricultural fields. They make contact with the Maxubis, a previously unknown Indigenous tribe with a “large population numbering in the several thousands” (161). The Maxubis appear healthier than other tribes, their culture more sophisticated. If such a tribe could exist undetected at such a distance from major rivers, then the prospects for a large, ancient civilization appear even more favorable.