This article takes a fresh approach to Walter Ralegh's published account of his voyage to Guiana, The Discoverie of the Large, Rich, and Bewtiful Empyre of Guiana (1596), using it as a case study through which to explore the fragility of sixteenth-century processes of knowledge production about new lands. The article revisits this famous account in order to scrutinise in more detail the types of evidence Ralegh used to support his claims that a rich and powerful empire lay ready to be conquered by the English in the Amazon. This new analysis of Ralegh's narrative highlights the continued centrality of reputational models of authority in early modern travel literature and examines the types of evidence that could be employed by writers to support their suppositions when witness testimony was lacking. Ralegh's narrative illustrates that systems of knowledge production centred on the New World were, at the end of the sixteenth century, still in a state of flux. New ideas about what constituted credible knowledge, from firsthand experience to the collection of material artefacts, competed with older frameworks of authentication and authority. By examining knowledge production in frustration, and by dissecting Ralegh's failure to present a believable vision of El Dorado, this article throws into starker relief the many pitfalls and difficulties that beset those who attempted to present new and credible knowledge about the New World.