Siena, Concistoro 2308: the cipher letters by key

The Archivio di Stato di Siena keeps the Sienese government’s cipher file as Concistoro 2308: fascicle 1, “Cifrari”, the filed keys (DECODE R4746–R4789), and fascicle 2, “Lettere in cifra”, the letters (DECODE R4790–R4814 and R1858), all photographed in the reading room and catalogued on DECODE as “1500–1599”. Aloys Meister counted 29 letters in 1902 and dated the first to 1421; 25 are photographed.

This page used to be one entry for the whole bundle, with a table of the pieces. Following George Lasry’s consolidated report, “The cipher documents of Concistoro 2308, fasc. 2” (17 October 2026), which deciphers most of the letters and groups them by key, each key now has its own entry. The headings below are his; piece numbers are the pencil numbers on the sheets. Under headings D, G and H each piece has its own key.

A. The Neapolitan royal key of 1413

Nos. 20 and 23 (R4808, R4811): a royal captain at Perugia to King Ladislaus, 30 March 1413, and two royal memoranda on the Marche campaign, about April 1413 (the years inferred from the context, not written). Read in full; key recovered from the ciphertext by George Lasry with CTTS and Claude. Seven name signs are open.

B. A Neapolitan court cipher of 1413

No. 12 (R4790): Naples, 10 March 1413, to Sforza: the King offers him a bride. The letter gives the day and the sixth indiction; the year 1413 is reconstructed from the indiction and the historical context. It is the earliest date in the file. Key recovered from the ciphertext by George Lasry with CTTS and Claude.

C. The filed key R4755 (Lucca, 1431)

Nos. 6 and 24 (R4795, R4812): Cristofano to the Signori, on the war over Lucca. Deciphered by George Lasry from the ciphertext alone; the filed key R4755 (fascicle 1) was found to match afterwards.

D. Fifteenth-century Sienese ciphers, one key each

No. 4 (R4793): Galgano Borghesi to Leonardo Benvoglienti, Naples, 12 May 1456. Key rebuilt here from a fragment on the letter.
No. 14 (R4802): Sienese envoys to the Priori, before 1429. Key recovered here from the ciphertext, in part.
No. 19 (R4807): Sienese envoys kept waiting by the S. Capitano, 9 March, 1440s. Not solved.
No. 21 (R4809): “Karissimo come padre”. Not solved.
No. 25 (R4813): a lord on the road to Casole. Key recovered here from the ciphertext.

E. A Florentine cipher of 1478

No. 11 (R4800): Donato Acciaiuoli to Lorenzo de’ Medici, Rome, 13 June 1478. Key recovered from the ciphertext by George Lasry with CTTS and Claude.

F. The imperial chancery cipher of 1496

No. 18 (R4806): Maximilian I and the Sienese orators, Pisa, November 1496. Key recovered from the ciphertext here and, independently, by George Lasry.

G. Sixteenth-century Sienese ciphers

No. 17 (R4805): Bartolomeo Tantucci, 25 August 1528, the “cifra di Balìa”. Key recovered from the ciphertext by George Lasry, about 85%.
No. 15 (R4803): Mario Bandini, Innsbruck, 4 January 1547. Key partly recovered by George Lasry, 75 of 240 signs; none of the filed keys fits, R4764 included.
R4794 (unnumbered; earlier given as “no. 5?”): the artillery slip, sixteenth century. Key recovered from the ciphertext by George Lasry; the four number codes 44, 26, 67 and 74 are open.

H. Pieces with an interlinear or separate plaintext

No. 9 (R4798): Castiglione and the King of Aragon, 1440s–50s. Key recovered by George Lasry from the decipherment below the lines.
Nos. 13 and 16 (R4801, R4804): the Pope and Bologna, c. 1527–29. Deciphered at the time (no. 16 is the clear copy); the key was recovered by George Lasry from the plaintext of no. 16.
No. 10 (R4799): “presura di Montepulciano”, deciphered at the time between the lines.
No. 7 (R4796): an orator at Milan to the Officials of the Balìa, 1450s. Not solved; the interlinear gloss gives nine values.
No. 8 (R4797): the Milan–Ferrara league slip, c. 1440–41. The report lists it as not yet deciphered; aligned here sign by sign, the memorandum on the same sheet is its decipherment.

I. Cleartext pieces and pieces not photographed

R4791, R4792, R4810: clear letters (R4810, no. 22, is a set of drafts in which numbers stand for key words).
R4814: fragment of a key.
Nos. 1 (1421), 2 and 26–28: in Meister’s count of 1902, not photographed. Only the Archivio di Stato di Siena can supply them.

Credits and sources

The grouping by key, the readings of nos. 20, 23, 6, 24, 12, 11, 18, 17, 9, 13 and R4794, and of no. 15 in part, and their datings are George Lasry’s (report of 17 October 2026 and corrections of 18 October, sent to Daniel Bourdeau). His method: CTTS for the transcription (in full, or correcting a transcription made by an LLM) and sometimes its built-in cryptanalysis, with Claude Opus 5.5 / Claude, and with GPT-6 Astra as well for nos. 6 and 24. He solved no. 18 independently and in full. Nos. 4, 14, 18 and 25 were broken here on 24 September 2026, no. 8 aligned with its decipherment here on 18 October 2026 (and again, independently, on 20 October). On 20 October his keys of nos. 17, 11 and 5? were run on this project’s own transcriptions of 24 September, made before his work: 92.9%, 94.4% and 93.1% of our signs give his reading; our transcription of no. 20 carries his reading at 71% against 15% for a wrong-plaintext control. Nos. 7, 19 and 21 are open. Sources: DECODE records R4746–R4814 and R1858; A. Meister, Die Anfänge der modernen diplomatischen Geheimschrift (Paderborn 1902), pp. 50–51; Archivio del Concistoro del Comune di Siena. Inventario (Rome 1952), p. 366.

Manuscript rights: Archivio di Stato di Siena. The collection’s key index, access notes and shared solvers: research/siena2308/.