The main purpose of this paper is to find out the author of the three Latin verses quoted by Pérez Galdós in his novel El 19 de marzo y el 2 de mayo (1873). After discarding Pérez Galdós himself and Sánchez Barbero (prima facie more likely) as authors, we have found the source in a Neo-Latin poem written in honor of Godoy and preserved in two handwritten copies, one in the Royal Academy of History and the other in Menéndez Pelayo's Library. The real author is the Enlightenment thinker Joaquín Traggia. This fact, in its turn, raises the problem of how Pérez Galdós could come to know any of these manuscripts around 1872. In addition, the manuscript text has been compared with Galdós's quotation in the printed version as well as in his own handwritten text. In sum, we have determined the authorship of the Latin quotation and its origin; we have considered the new literary context of these verses in Pérez Galdós's novel; and lastly, a new, amended edition of such verses is proposed. [ABSTRACT FROM AUTHOR]