The sources of the Hispanic rite, mainly preserved within the archives of the Toledo Cathedral and the National Library of Spain in Madrid, constitute a distinctive corpus, different from other manuscripts of this ancient rite. The presence of an exclusive notation, their comparatively decayed appearance in terms of handwriting, the existence of a distinct liturgical tradition, and finally, theories suggesting that its origin could be much later than that of other sources, make this group of manuscripts an object of particular interest for reconstructing the history of Hispanic chant, due to the questions their mere existence make us consider.