A Plot to Betray the Castle of Nice: an Undeciphered Imperial Cipher Report of July 1549 in the Gonzaga Papers at Modena

A two-leaf cipher letter in the Biblioteca Estense Universitaria, Modena (Autografoteca Campori, Lettera K, "Karl V", sfasc. IV, cc. 131–132), filed among Charles V's letters to Ferrante Gonzaga, is catalogued as an undated "lettera cifrata" without decipherment. We show that it is written in the numeric syllabic cipher of Charles V's chancery of 1548–1549, reconstruct the working rules of that cipher from a sibling letter whose contemporary decipherment survives (Charles V to Ferrante Gonzaga, Ghent, 15 July 1549; cc. 40–42), and add a rule not previously recorded (a superscript 13 marks a null). The key yields a heading "[copia de la letra] del embaxador en Francia" and a closing date "a doze de julio de [mil] quinientos y quarenta y nueve". The leaf is the ciphered copy of the imperial ambassador's report of 12 July 1549 that Charles V enclosed with his letter of 15 July on "la empresa que los franceses quieren hazer del castillo de Niza". The report describes how men of the garrison of the castle of Nice had been promised money and four pays to hand the castle to the Count of Tende, governor of Provence, with a force of [twelve galleys?] and three hundred soldiers; the Constable of France is named, and the warning is passed on to the imperial ambassador at Genoa. Version 1 gives the identification, the key and a provisional reading of the passages that can already be read with confidence; a full line-by-line edition will follow in version 2. Files: preprint (PDF), working transcription of cc. 131r–v, and the reconstructed key. No manuscript images are reproduced.