This article seeks to analyze the use of Laymundo Ortega as a source by Bernardo de Brito in the Monarchia Lusitana and answer the question what is it for that the chronicler employs the forged source which until then was completely unknown. After an introduction on the fictional figure of Laymundo and his manuscript begins the analysis of his use in Brito's chron-icle. We work from the primary source on by analyzing the references to Laymundo and by putting them in the context of the peninsular chronicles of that time. The main conclusion of our work is that Brito uses Laymundo in order to put Por-tugal in a preeminent place in the origins of Iberian history. The source of Laymundo is used to prove the arguments for which are no sources available and which, therefore, had not appeared this way in other chronicles.