Relations of Guerreiro
In the early 17th century, Portuguese Jesuit missionary Father Fernão Guerreiro traveled throughout the East Indies, China, Japan, and Africa. He records this journey in letter and reports, later collected and published in this three volume Relação, which relates the entirety of his missionary endeavors with the Benedict Goes and the Society of Jesus. The sole complete text resides in the British Museum Library, though it has been reprinted.
Of course one of the central missions was to glean information about the kingdom of Prester John. In the text, Guerreiro dismisses Ethiopia as the site of Prester John. He correctly ascribes the misplacement of Prester John in Ethiopia to the eagerness of the Portuguese emissaries sent there, who conflated the site of Christians with their presence in the kingdom of Prester John.
Instead, Guerreiro believes that Prester John was “the Emperor of Catayo [China]." He explained that the conversion of the Catayo to Christianity occurred because of St. Thomas and his disciples (who made it farther east than Thomas himself).
