This paper focuses on the description and analysis of three codices from Biblioteca Nacional in Madrid with the aim of redefining their origin, dating, authorship, and content. Connecting their production to the environment of the Sacromonte affair and identifying Pedro de Castro’s hand allows to expand what was known so far about his attempts to learn Arabic and delve into the most controversial aspects of the Lead Books. The grammatical and religious contents, in addition to the copious marginal notes linked (...) to the sources he used, provide valuable information on his selection of works. Grammatical materials such as al-Āŷurrūmiyya, of which different versions are preserved in these codices, were being published in Rome and Leiden and would be widely disseminated. The building up of his library, to which these codices must have belonged, runs in parallel to the construction of an orientalist knowledge in modern Europe. (shrink)