«During the course of the Church’s bimillenial history, pontiffs are thought to have produced between 30 and 40 million documents. This immense bulk of original correspondence is treasured in secular and ecclesiastical archives all over the world. However, in order to preserve a memory of the texts, the various offices and officers of the Roman Curia in charge of drafting and sending the documents to their respective addressees, were accustomed to writing their contents in specific volumes, papal registers. However, so-called “register copies” are not just a mere reproduction of the document’s contents: in the eyes of the pontiffs they held (and still hold) an official value.
Just a few examples are sufficient to explain the importance of these registers and their contents. A recipient may have required a document to be sent to him again: if he was unable to produce the original copy because he had lost it for diverse reasons, the papal Curia drafted a new document based on the text contained in the register, which served as the official exemplar. Another notorious case is that of the infamous Exsurge Domine bull addressed to Martin Luther by Leo X; this document’s many originals, which were sent all over Germany, have been mainly destroyed. Under these circumstances, the bull “copied” in Leo X’s Vatican register gains a significant value, for it preserved the official drafting of a document that has become rare or has been lost due to the adverse historical conditions during which it was issued.
Sometimes, registers can even provide noteworthy information regarding the phases in the creation of original documents. This is the case with the Inter cetera bull, by which Alexander VI acknowledged the Spanish royals’ dominion over the lands in the New Word. In this pope’s Vatican registers, two different versions of the document are to be found; the first one omits an indication of the geographical allocation of the new lands granted to the Spanish sovereigns, while the second one dwells in carefully describing the confines of the new dominions. What had happened? When the first version of the bull was sent, Spanish emissaries deemed the document incapable of eventually warding off the king of Portugal’s territorial claims; therefore, the papal Curia drafted a second version that met the Spanish sovereigns’ needs. Traces of these “negotiations” are to be found in Alexander VI’s registers, while the original parchment, that only contained the second version of the bull (preserved at the Archivo General de India, Seville), doesn’t make any suggestion in regard to the complicated drafting of such a relevant document for the history of the American continent.»