Descripción del virreinato del Perú, en particular de Lima was written in Spanish during the first half of the 17th century by an unknown author. The manuscript was found in Paris and presented by Riva Agüero in 1914. Underlying the 2009 and 2013 editions is the thesis that the anonymous author would have been a Portuguese New Christian who travelled through the Spanish empire during the period of union between the Iberian thrones in parallel with the established legal separation. Just as Pratt used the Andean manuscript of Guaman Poma de Ayala in applying the concepts of “contact zone”, this article utilises her theories to try to understand why this supposed Portuguese individual used the Spanish language in his description of the territory of ancient Peru.