Louis XIII to Philippe de Béthune, 30 June 1629 (BnF Français 3675)

01 The letter

Shelfmark	BnF Français 3675 · Louis XIII à Béthune, 30 juin 1629
Sender	Louis XIII
Recipient	Philippe de Béthune
Date	30 June 1629
Language	French
Report status	1/2 pages transcribed; 1 more in part; Partly deciphered
Ciphertext	177 elements, 166 identified (93.8%).

02 The key

59 mapped symbols; 11 unidentified.

George Lasry’s reconstructed key table — George Lasry’s reconstruction of the key, as drawn in his report (p. 101). Image: George Lasry, BnF cipher research (10 Oct 2026); manuscript: Bibliothèque nationale de France, Français 3675, Gallica btv1b9059466m view 108.

03 The decipherment

Manuscript lines with the cipher, from George Lasry’s report — The manuscript lines of the excerpt (f53r, three complete cipher-bearing rows and preceding cleartext), from the report, p. 102. Image: George Lasry, BnF cipher research (10 Oct 2026); manuscript: Bibliothèque nationale de France, Français 3675, Gallica btv1b9059466m view 108.

f53r, three complete cipher-bearing rows and preceding cleartext

vous les fassiez valloir et peser à sa Saincteté y adjoustant de plus la recommandation des grands services de mon cousin le cardinal de Richelieu son frere de qui le [passage rayé] la conduicte et les actions sont

Translation. you should make these qualities count and carry weight with His Holiness, adding also the recommendation of the great services of my cousin Cardinal Richelieu, his brother, whose [cancelled text] conduct and actions are…

04 Plaintext and other sources

Where a decipherment or clear copy already existed, as George Lasry gives it:

Interlinear plaintext: Interlinear plaintext on f53r; shared signs checked against interlinear passages on f83r–v and f136r.

05 Our check

This result is George Lasry’s. This project did not re-solve the cipher: it checked one sample against the Gallica image and recorded what it found.

Batch B. Image checked: https://openapi.bnf.fr/iiif/image/v3/ark:/12148/btv1b9059466m/f108/full/1600,/0/default.jpg
Folio matches the report: yes; cipher present: yes
What we checked: f53r: clear "vous les fassiez valloir et peser a sa Ste y adioustant de plus la recommandation des grands" + interlinear over cipher "services de mon cousin le cardinal de Richelieu son frere de qui la [struck] conduite et les actions" = his excerpt; next 4 cipher rows uninterlined (his own decipherment, not checked)
Verdict: confirmed (method key recovered based on adjacent plaintext, extent partial). The check is a sample, not a re-solution.
Notes: Addressed "Monsr de Bethune"; Archbishop of Lyon (Alphonse de Richelieu) cardinalate 1629 fits. 93.8%, partly deciphered.

06 Sources

George Lasry, with ChatGPT Astra 6 and Anthropic Opus 5.5, BnF cipher research, 10 October 2026 (sent to Daniel Bourdeau on 13 October 2026 for publication here), p. 101; his other items are listed on his contributor card.
image checked in the spot-check
The working folder: targets/bethune1629/ (his entry as extracted from the report, our spot-check, profile.json).