Un manuscrito inédito de la Biblioteca del Palacio Real de Madrid proporciona interesantes noticias acerca de la desconocida figura de Jerónimo de Borja y de sus invenciones e ingenios bélicos, ofrecidos al monarca español Feli.pe II en vísperas de la empresa de Inglaterra. En el presente trabajo se aborda sólo su actividad profesional al haber sido ya objeto de un anterior estudio para esta misma revista la faceta humana del personaje.

An unpublished manuscript of the Library of the Royal Palace of Madrid, provides sorne interesting news on the unknown figure of Jerome of Borja and his inventions and war engines, which were offered to the Spanish King Philip the Second on the eve of the campaign against England. This research only deals with his professional activity, for his human features have been studied in a previous article, published in this same section.