Una bula incunable desconocida del Instituto Valencia de Don Juan. Nuevos datos de la imprenta salmantina

The discovery in the Instituto Valencia de don Juan of an until now unknown incunabular bull of crusade acquired by the Countess of Oropesa, is a good opportunity to study its provenance and identification. This bull was printed in Salamanca in the offices of Juan de Porras and Juan de Montejo, but some pieces of information retrieved in several Spanish archives have allowed the authors to reconsider the history of the printing presses in Salamanca, as intricate as enigmatic, since there are some clues that point to the presence in the same place and time of at least other two workshops, those of Juan de San Vicente and Rodrigo de Escobar.