In the following article we present an unpublished and unknown text of Galician discoverer Pedro Sarmiento de Gamboa. The letter, wrote in Latin, was send to Lord Burghley, the first minister of Elizabeth Tudor. Its content links chro-nicles and legends of Spain and Galicia to the genealogy of Sarmiento de Gamboa. Here, we offer the biographical context of the letter, a brief study of the sources, apart from the transcription of the original and the translation of the text into Spanish.