The Farnese letter | Simon Klee

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Sep 16, 2026
The Farnese letter

In April 1542 a letter left Rome for the court of Charles V in Spain. On its
first page the Italian stops in the middle of a line and digits begin:

Figure 1. The opening of the cipher, f. 70r. Archivio Apostolico Vaticano
(AAV), Segr. Stato, Spagna 1A, photograph supplied through
DECODE record 92.
Detail enlarged from the photograph.
Read with the key recovered below, the first ten digits group like this:
73 4 57 4 9 03 5
d o p o · l a

Dopo la, "after the". The 9 stands for nothing: it is a null. The
difficulty is deciding where each code ends. 73 is d, but 7 3 is also
two letters, n m. Even with the key, a run of digits can be read more than
one way.
Two problems follow: finding the key without knowing where one code ends
and the next begins, and then, once a key exists, telling the writer's
words from a plausible guess.
The letter
The sender was Cardinal Alessandro Farnese, grandson of Paul III and, at
twenty-one, head of the papal secretariat. The recipient was Giovanni Poggio,
bishop of Tropea and nuncio, the Pope's ambassador, at the Emperor's
court.1 The letter opens in ordinary Italian: Poggio will have heard
by word of mouth from Giovanni Ricci da Montepulciano about la materia della
pace, the peace between the Emperor and France, so Farnese will not repeat
it. Montepulciano had returned from Spain in February with the Emperor's
terms and had left Rome for Spain again in late March.2
Montepulciano's name is also on a cipher key. Aloys Meister's 1906 study of
papal cryptography prints, among the old ciphers of the papal secretariat, a
key headed Cifra ultima con Mons. Poggio mandata per il Montepulciano: the
latest cipher with Poggio, sent by Montepulciano. Meister dates it 1538–42.3
The letter fills eight pages on four leaves, 70r to 73v in the archive's
numbering: r for the front of a leaf, v for the back. Page 70r is
cleartext for most of its length. Then the digits take over in the middle
of a line and fill the whole of pages 70v to 72r. On 72v they surround a
cleartext passage about church business and news from Ancona, "fresh and
from a good source". The cipher ends on 73r, and the rest of that page is
clear. Page 73v is clear and dated Da Roma alli X[?] di Aprile 1542: the
day is a Roman numeral beginning with X whose remaining strokes lie under a
flourish, still unread. What is in clear is the frame; the instructions are
in cipher.4

Figure 2. Ff. 70r and 70v. AAV, Segr. Stato, Spagna 1A, through
DECODE record 92, public
previews. The change from prose to digits comes near the foot of 70r.
The cipher continues across the next page.
Ludwig Cardauns cited this volume in his 1912 collection of the nuncios'
reports, but his selected correspondence does not include this letter.5
In July 2019 George Lasry set the text as Part 5 of the Vatican Challenge
on MysteryTwister, a site of cipher puzzles: key unknown, plaintext unknown,
language probably Italian.
In their study, published online in 2020, Lasry, Beáta Megyesi, and Nils
Kopal still listed the Spagna 1A material as unsolved. Their digit-frequency
analysis placed it in a separate cluster. They compared another part of
the collection, IA-1, with Meister's Poggio key, without success, and thought
this letter, IA-2, used a different key.6 On 16 September 2026,
the challenge page still displayed zero solves.7
The search began with a public transcription, now distributed with the
DECODE record and the challenge. Its header credits EHum, dates the
transcription 9 January 2016, and records about six and a half hours' work
on the eight pages. The transcription contains 6,577 cipher digit positions:
44 recorded as ?, unreadable, and 207 with a mark above them, mostly dots.
There is no consistent word division. The full ciphertext
is reproduced as text, with its page and line breaks. The counts and searches
below used this public transcription. I checked it against the larger
photographs later.8
What the counts show
In the public transcription, digit 7 makes up 17.5 percent of the text and
1 only 3.1. A few pairs are far more common than chance: 80 occurs 349
times, 57 317, 27 263, 03 258, 73 220. Doubled digits are nearly
absent: 00 six times, where independent digits would give about 117; 11
three times; 44 twice. And the digits alternate between two groups,
4 5 6 8 and 0 1 2 7 9, with 3 belonging to neither: after 73, for
instance, the next digit is 6, 8, 4 or 5 in 93 percent of cases.9

Figure 3. How often each digit follows each other digit in the public transcription.
The five pairs in bold turned out to be the codes for t, p, c, l, and d. The
pale diagonal is the avoidance of doubles. Author's computation from EHum's
2016 transcription.
That looks like consonants and vowels taking turns. But it does not decide
whether 73 is one code or two frequent neighbors, and no fixed rule of
cutting, such as pairs at even positions or certain digits always beginning
a pair, gave a consistent result.
The papal ciphers of the 1540s used several designs. In some, one digit
stands for several letters and the reader chooses. In some, pairs spell
syllables. One 1545 key writes the vowels as pairs and the consonants as
single digits.10 I tried these designs with earlier versions
of the search, without obtaining readable Italian.11 The design
that fitted was a simple one also printed in Meister's collection: every
letter has one code, of one or two digits, and the reader tells them apart
by context.

Figure 4. A key of that design: Meister no. 7, for Alessandro Vitelli,
dated by Meister to 1546. Single digits for some letters, pairs for the rest,
one null, a few words. Aloys Meister, Die Geheimschrift (1906),
p. 179;
Getty Research Institute copy, digitized by Internet Archive. Cropped from
the printed edition.
The search
I searched for the key and the code boundaries together. An outer search
changed the assignments of letters to codes. For each candidate key, an
inner decoder searched for a good way to divide the digits and read them.
The outer search could then compare keys by how well their readings scored.12
To judge those readings, I trained a character model that estimates the
probability of each letter from the four before it: a five-gram model. It
trained on about 4.9 million letters. Most came from Machiavelli,
Castiglione, and Vasari on Wikisource. About 720,000 came from Italian-looking
lines extracted from the OCR of Cardauns's Nuntiaturberichte aus Deutschland
I.7, which includes correspondence of the Farnese secretariat from 1541–44.
That volume does not print this letter.13 I lower-cased the text,
stripped accents, folded v into u, deleted h, and collapsed doubled
letters. These were guesses about the clerk's habits, and they turned out
to match: the letter writes tute, esendo, facia; its key has one code
for u and v and none for h.
A letter sequence absent from the corpus still needed a chance. The model
blended the counts for a four-letter context with estimates from shorter
contexts, down to individual letter frequencies. This smoothing let it score
unfamiliar names and damaged words without ruling them out altogether.14
Reading a candidate key
The decoder walks the digits from left to right. Under the key eventually
recovered, the opening has these two possible paths, among others:
Digits 7 3 4 5 7 4
One path 73 4 57 4 d o p o
Another 7 3 4 57 4 n m o p o
The first path consumes 73 at once and emits d; the second consumes 7
and 3 separately and emits n m. Each emitted letter adds its base-10 log
probability to the path's score. The letters that follow can favor one path
over the other, so the decoder keeps several partial readings alive.
Each partial reading is a state, which records the position in the digits,
the last four emitted symbols, and the score so far. If two paths reach the
same position with the same language-model context, their possible
continuations are identical: only the better-scoring path needs to survive.
Among different contexts, the decoder keeps the eight best at each position.
This is a beam search. It is an approximation: a path discarded early cannot
recover when later letters would have made it convincing.
In the successful searches, I set aside the digits with a dot or comma above
them and cut the text at those places and at unreadable digits. Each
fragment began with a fresh language-model context. The key received the
sum of its best surviving fragment scores, including penalties for nulls
and digits it could not decode. The dotted codes would come back once the
letters were known.15
Changing the key
The outer search began with random assignments, favoring codes that occurred
more often. It could swap two assignments, move one to an unused code, or
turn off an optional unit such as a null. It accepted any improvement. It
could also accept a worse key, with a chance that fell as the run went
on. This is simulated annealing. Accepting worse moves lets the search
escape a key that beats its immediate neighbors but is still wrong. I
repeated the search from fresh random keys. Each repetition is a
restart.16
The first search to produce recognizable Italian gave this opening, with
underscores marking the null:
dopo_lapartitadelmontepinmcian_il_manon

Dopo la partita del Montepulciano, "after Montepulciano's departure". The
cleartext on the same page mentions his departure. Further along were
prepararsi contra … del turco, cento naui, ungaria, ridolfo gonzaga,
forteza di luzara, mons. di granuela.
Much of the rest was still garbage. This search had been allowed a pool of
optional word codes, and it used them to explain away inconvenient digits.
Searches that were allowed several nulls declared three frequent digits
meaningless. Allowing two codes per letter also gave high scores for worse
text. Yet four of the first search's six restarts had given the same codes
to the same eighteen letters, the whole alphabet the clerk used. The letter
assignments were stable even while the extra codes spoiled the reading.17
I tightened the search to one code per letter, at most one null, and no
word codes. I also retrained the Italian model with word spaces removed.
A model trained on del quale expects a boundary after the l, but the
decoder presents it with delquale. The unspaced model learns the letter
sequences across those boundaries. With these changes, the search reached
the same letter key from two of three restarts. The third stopped at a worse
key.
Table 1. Settings for the tightened search.15

Setting in the tightened search
Value

Candidate codes
Single digits and pairs occurring at least three times in the scored fragments

Breaks in the input
203 above-dot/comma tokens and 44 unreadable tokens; one belongs to both groups

Input after those cuts
219 scored fragments; 6,331 retained digits18

Beam width
Eight states per digit position

Proposal attempts per restart
500,000

Penalty per null
1; emits no letter and preserves context

Penalty per undecodable digit
4, when neither the single digit nor the available pair has a code

The penalties discourage a key from improving its score by leaving text
unread. Scores below divide the penalized total by the retained-digit count.
Nearer zero is better. They rank the keys found under these settings, rather
than measuring the probability that a reading is correct.

Figure 5. The recovered key. The single digits 4, 5, 6, and 8 are the vowels
o, a, i, and e that the pairs table showed taking turns with the rest.
Author's reconstruction.
Checking the key
Could the same key be recovered without the opening name? I split the text
after its third cipher page and solved each half on its own, from random
assignments. Every restart recovered the same eighteen letters and the
null.
I also enciphered known Italian with two invented keys of the same design:
one synthetic cipher was clean; the other had digits substituted or marked
unreadable. Finally, I shuffled the real ciphertext and searched that. These
controls used the tightened search settings.
Table 2. Recovery and control runs.19

Input
Result
Score per retained digit

Whole letter
Same eighteen letters and null in two of three restarts
−0.783; third restart −1.150

First and second halves, solved separately
Same letters and null in all twelve restarts, six per half
−0.777 / −0.785

Clean synthetic cipher
Letters and null recovered in all three restarts
−0.630

Synthetic cipher with digit substitutions and 44 digits marked unreadable
Letters and null recovered in all three restarts
−0.692

Shuffled real ciphertext
Best of two restarts
−1.351

The synthetic tests did not recover the word code for et, which the
letter-only search could not express. Their Italian also later proved to
overlap in part with the model's training text. All the controls share the
Italian model and its habits, so the check I trust most is the split: either
half of the letter alone yields the letter key and null.
Lasry and his coauthors reported that, in their project, variable-length
homophonic keys (those allowing several codes for a letter) had required
matching plaintext or an already documented key. The simpler, monoalphabetic
key used here came out of the digits.20
Dots and the null
With the letters fixed, the decoded text around repeated dotted pairs
revealed their meanings. A 27 with the dot on its second digit, the 7,
sat where Marchese has its che, and wherever the sense wanted che,
"that". A 72 dotted on its second digit too sat where carichi,
"burdens", has its chi; a 57, dotted the same way, where non si vede,
"one does not see", has its non. With the dot on the first digit instead,
the same pairs gave qua, que and qui.

Figure 6. The dot on the first digit gives qua, que, qui; on the second, che, chi,
non. Three more dotted pairs are titles: Sua Santità, Sua Maestà, Vostra
Signoria, written here as the cleartext abbreviates them. Author's
reconstruction.
The search alphabet had also included q, which the cipher does not need
as a separate letter. In the tightened full-text run it occupied 81.
The decoded contexts gave that code the reading et, "and". The null 9
is not a consistent word divider. It ends some words and not others, appears
inside words (tu·te for tutte, the dot marking the null), and is used in
con, written 27 4 9 7. It can prevent misreadings: 8 9 0 reads
e s, where 80 would be read as t.21
What the digits say and what the model wants
Recovering the key does not settle the text. The sequence 0 5 7 8 0 5
occurs four times in the letter. Under the key it has two Italian readings.

Figure 7. The digits 0 5 7 8 0 5 under the key: santa or spesa.
Author's diagram.
My first reading, in three of the four places, was la santa [impresa], the
holy enterprise, with a word supplied. The surrounding argument calls for la
spesa, the expense, every time: the Pope will contribute what he can to the
expense; the ships may not be ready in the year the expense is for; he will
pay his share of the expense against the Turk.22
Reading through errors
Some passages suggested errors in the digits themselves. In Montepulciano's
name, the transcription gave 2, which the key reads as r, where the name
needed u. I wrote a second decoder to compare literal readings with readings
that required small changes to the transcription. The key, now including the
dotted codes, stayed fixed.
The key search had cut the text at unreadable and dotted digits. This decoder
worked through the cipher on each page, keeping the language context across
unreadable places. It preserved the transcriber's qualifications:
2? meant a doubtful 2, 1/2 offered two readings, and ? meant an
unreadable digit. Dots, commas, and dashes above the digits were retained too.
At each position, the program compared the next digit or pair with the codes
in the fixed key. An exact match cost nothing. Where nothing matched, it
could propose a different digit or a changed above-mark. It could also drop
a digit, supply the missing half of a pair, or insert a single-digit letter
code. I assigned different costs to these operations so that filling a known
hole was easier than contradicting a digit the transcriber had read without
qualification.
Table 3. Edit costs in the fixed-key decoder.23

Proposed operation
Cost in base-10 log units

Keep the digit, or the first offered alternative
0

Fill an unreadable ?
0.3

Choose the second offered alternative
0.5

Substitute a listed look-alike for a digit marked uncertain
1

Substitute a listed look-alike for a digit not marked uncertain
3

Substitute a digit outside the list
6

Supply or ignore an above-dot
3

Ignore an above-comma / above-dash
2 / 1

Insert or drop a digit
5

The look-alike list included such confusions as 1 with 2, 3 with 5
or 7, and 0 with 8 or 9. These were hand-set costs, not measured
error probabilities.
The score combined the two kinds of evidence:
reading score = sum of letter log probabilities − sum of edit costs
Code divisions and edits were searched together. A changed digit might join
the next one into a pair, changing both the number of letters emitted and
the context for the letters after them. As before, the decoder kept several
partial readings alive and recorded the choices behind each one.
At the disputed digit in Montepulciano, keeping 2 emits r without an
edit cost. Choosing 1 emits u but subtracts three from the score. That
choice also changes the model's predictions for the following letters, until
the changed letter has passed out of its four-letter context. The gain in
the Italian score was enough for u to win. The edit list records:
Source Change Letter Context
2 2>1 u elmontep [u] lcian il
This repairs the middle of the name, but its final o is still absent.
Another proposal supplied the dot that turns 72, b, into 7̇2, que.
The result reads in quele di Ungaria, "in those [affairs] of Hungary", in
place of in ble di Ungaria.
The same scoring rule could damage a passage that already read correctly.
On 71r it proposed reading an 8 as the null 9 and regrouping the nearby
digits, turning a le sue sei galere, "his own six galleys", into
al tuti galere. I refused that change. The model judged short letter
sequences. It did not know how many ships the Pope had or follow the
argument about paying for them. A gain large enough to pay for an edit
could still produce the wrong reading.
The edit list tied each proposal to its source digits and surrounding text.
I could accept or reject a reading and locate the disputed digits in the
photographs.
Table 4. Changes proposed by the decoder.23

Type of proposed change
Value

Fills of unreadable digits
44

Other proposed operations, including choices of an offered alternative
126

Other operations divided by the public transcription's digit count
1.9%

The totals include rejected proposals. Whether an apparent error belonged
to the transcriber, the clerk, or the reader still required checking against
the page.
The edition
The edited text, the edition from here on, uses
square brackets for conjectural letters. A
digit-by-digit alignment behind it records what
brackets cannot show: ignored dots, dropped digits, digits read as the null.
The alignment makes departures visible; it does not make the readings true.24
To test the conjectures, I gave the key to two readers, each a fresh run of
the GPT-6 Astra language model, together with the digits of one page decoded
literally under it: 72r for one and 71v for the other, the two pages with the
most departures. Each was asked for a continuous reading and an account of
every place where it left the literal decode. Each recovered its page's
argument and many of the edition's words, and each caught something the
edition had wrong.
On 72r the edition had left a gap and supplied [che potrà] on no digits
at all. The reader found that the twenty digits behind that gap read verà
la magior piena exactly, "the greater flood will come". With the lost verb
recovered, the supplement was unnecessary. On 71v the edition had the Emperor
knowing that the Pope's forces are small in themselves, S.M.tà s[a] che,
at the cost of one 2 read as 5 and two digits read as nulls. The
reader's o[l]tre che, "besides the fact that", needs one ignored dot and
one missing digit, and fits a sentence that goes on to say the forces are
also divided. Both were adopted. The readers were independent of the
edition, not of the key or the transcription. Like the edition, they had
never seen the page.25
The page
I checked the disputed readings against photographs of the manuscript.
In Montepulciano's name, the decoder wanted a u where the transcription
gave 2, the code for r. On the page, the disputed digit is a single
stroke with a foot: the clerk's 1, which gives u.

Transcription 57 2 03 27
Page 57 1 03 27
Reading p u l c
Figure 8. F. 70r, second cipher line. AAV, Segr. Stato, Spagna 1A,
through DECODE record 92; enlarged detail. The name was already a plausible
correction from the Italian. The photograph shows why the digit was misread.
The clerk often joins one digit to the next. The top bar of a 7 runs into
the preceding digit. The foot of a 1 can make it look like a 2. In a small
pilot, I showed four short strips to three vision models. They made roughly
12–18 percent digit errors, often on those same confusions. That pilot was
too small, and its scoring too different, to establish a character-error-rate
comparison with the public transcription.26
I needed a way to compare a doubtful digit with the clerk's other examples.
I wrote a program that first straightened each cipher line and removed the
handwriting's slant. It looked for cuts in the white gaps and the thin joins
between digits, then fitted the transcription to those cuts. Each transcribed
digit became a provisional label on a small image. A 2 in the transcription
meant "this image is an example of a 2", even where that label would later
prove wrong.
A seven-neighbor classifier compared each image with examples from other
lines. It used their shapes and proportions to find the seven closest
matches, then combined their labels to propose a digit. Leaving out the
current line kept a digit from being compared with itself or a neighboring
piece of the same joined stroke.

Figure 9. The glyph transcribed as 2 in Montepulciano, followed by its seven nearest
matches from other lines. These are the straightened, normalized images used
for comparison. The labels come from the public transcription. Author's
analysis of AAV, Segr. Stato, Spagna 1A, ff. 70r–73r, photographs supplied
through DECODE record 92.
The classifier agreed with the transcription on 90.5 percent of the glyphs,
and on 98.9 percent of the roughly two-thirds of glyphs it read most
confidently. Those figures measure agreement with the old labels. To find
transcription errors, I needed the disagreements.27
For each suspect, a review sheet put the digit in its line of handwriting,
beside the seven matches and a reference sheet of the clerk's forms from
0 to 9. I checked the ink and recorded the reading, the reason, and how
certain it was. I examined all 196 ranked suspects this way, together with
every line where the segmentation had found a different number of digits
than the transcription. Where the classifier doubted a
digit the edition had left alone, my reading mostly sided with the
transcriber: a smear could flatten a 3 into the shape of a 5, or the
next digit's stroke could give a 7 the base of a 2.28
Some errors were in the number of digits. On 71v the transcription repeated
the five digits that read anco, "also". The photograph has them once.

Transcription 5 7 2 7 4 5 7 2 7 4
Page 5 7 2 7 4
Reading a n c o
Figure 10. F. 71v, fourth cipher line. AAV, Segr. Stato, Spagna 1A,
through DECODE record 92; enlarged detail. The edition had already dropped
the second anco as a repetition by the clerk. The repetition was in the
transcription.
The check found five such doubled groups, totaling twenty-one digits not
on the page, as well as fourteen omitted digits and two swapped pairs. Some
of the extra digits had supplied words for the edition: sendosi [c]osì firmat[o]
became sendosi firmat[o], "having been agreed", with no così, "thus".29
On 70v, a dot and two hooked 1s closed a gap in the account of the naval
expenses. The transcription had missed the dot over the 7 and read both
1s as 2s.

Transcription 27 2 6 9 2 5
Page 27̇ 1 6 9 1 5
Reading che u i · u a
Figure 11. F. 70v, third cipher line. AAV, Segr. Stato, Spagna 1A,
through DECODE record 92; enlarged detail. With 1 standing for both u and v, this reads
che vi va: the full phrase is della spesa che vi va dentro, "of the
expense that goes into it". The dot in the reading row marks the null 9.
Other corrections confirmed letters the edition had supplied. In è s[t]ato
on 70r and aiu[t]o on 72r the transcription has 0 8 where the page has
80, the code for t. The s of stato still has no digit behind it: the
page has the null 9 there, so the edition now reads è [s]tato. Other
bracketed letters, ris[p]osta and sol[d]o among them, stand on the page
as the edition read them. Some letters the edition had supplied turn out to
be on the page: the n of Massimi[li]a[no] is a 7 the transcription
read as 9; the c of ues[c]ou[o], vescovo, bishop, is a 2 the
transcription skipped, completing 27; the i of Dor[ia] is a 6
dropped at a line end.
On 72r the edition had conte[n]ti with a supplied n. The page has a 7
where the transcription has 4, and contenti is exact. On 70v the
conjecture [ca]pitarà il bisogno is withdrawn: the transcription's 8 is a
1, and the edition now reads [d]'ovunche più sarà il bisogno, "wherever the
need will be greater". The initial d remains conjectural. Other checks went
the other way. On 73r the edition had [ne]l qual luogo by changing a 6,
but the 6 is plain and the text reads il qual luogo. On 70r the 2 the
edition read as 3 for contra [l]'armata has the clerk's usual 2 form:
if l was meant, the clerk miswrote it.
One correction changed who had asked for a public announcement. Under the
archive stamp on 72r, the corrected digits give la S.M.tà [h]a voluto,
"His Majesty has wished", where the edition had read S.S.tà, His Holiness.
The Emperor had asked for the Hungarian subsidy to be offered publicly at
Speyer, in the Pope's name.
The castle's name remains conjectural. Where the edition had supplied
[Poviglio] from the Gonzaga genealogy, the corrected digits give
a pore in · pui ·, with the dots here marking nulls. The edition now reads
a porre in P[o]ui[glio], "to settle in Poviglio". The missing letters still
come from the proposed historical identification.30
I also checked the dots wherever the edition added or ignored one. In
risposta, the mark transcribed above a 7 was the top bar of the 5
before it. Other apparent dots belonged to strokes from the line above. In
Marchese, the dot was real but on the wrong digit of the pair: the clerk
had written qua where the name needs che.29
The corrections judged sure or probable went into a new transcription.
Unresolved readings stayed open. I then aligned the edition against those
corrected digits.31
Table 5. Source digits consumed by the edition's alignment. Both the
transcription and the edited reading changed after the page check.32

How the edition reads the digits
Before the page check
After

Digits in the transcription
6,577
6,562

Read exactly under the key, including nulls
6,216
6,358

Read with a recorded departure
300
170

Left in gaps
61
34

Blots, the archive stamp, and smears along the page edges leave some digits
and dots unread. I have not checked every glyph the classifier accepted,
and substitutions between unlike digits still need another look. The day
of the month also remains unread.
A contemporary copy in clear could help with the remaining readings. The
Archivio Apostolico Vaticano searched the index to a register cited by
Cardauns, but found no entry for an April 1542 letter from Farnese to
Poggio.33
What Farnese put in cipher
The summary below follows the proposed decipherment. Its quotations
translate the edited Italian. Gaps and conjectures remain in the edition.
After Montepulciano's departure, the imperial ambassador in Rome, the
Marqués de Aguilar, has been with the Pope and brought him Andrea Doria's
advice on arming against the Turkish fleet, and a request for help.34
The Pope will hold back nothing within his means, at sea or in Hungary,
wherever the need turns out to be greater. But nobody yet knows whether the
greater danger will come by land or by sea, and he will not decide where to
spend, "so as not to fall into the error of spending in vain in one place
that needed it less, and then be unable to help the other." He leaves that
to the Emperor's prudence.35
He has two doubts about the plan to arm a hundred ships. He argues that a
mixed fleet of galleys and sailing ships has never done well. And a hundred
ships would take so long to fit out that they would hardly serve this year,
the year the money is for. He will pay his share anyway, beyond his own six
galleys.36
The soldiers on his ships must be his own. The Papal State is full of good
soldiers used to going to war. Unless he keeps them employed, no edict in
the world will stop them taking pay from whoever offers it, to the
disturbance of his own state and no advantage to the Emperor. He means, too,
to stay neutral so that he can broker the peace, and to give nobody grounds
to say he pays for anything but defense against the Turk.37
Then there are the other commitments. The Hungarian subsidy, which Charles V
asked for at Lucca, was settled in Rome with the imperial minister Granvelle.
At the Emperor's request, the bishop of Modena, Giovanni Morone, has now
offered it publicly, in the Pope's name, at the Diet of Speyer, the assembly
of the German estates then in session. The enclosed extract from Modena's
letter shows that those at the Diet are not content and ask for much more.
Ancona, Civitavecchia, the other ports, and the guard of Lombardy also need
money. The Pope cannot yet say what more he will give on either
side.38
Finally, Ridolfo Gonzaga, son of Gianfrancesco, is said to have taken a
commission from someone whose name is still unread. He gathered infantry at
Luzzara, his brother Massimiliano's castle in Mantuan territory, then moved
to his own castle in the territory of Parma and began to fortify it, either
because the Marchese del Vasto, the governor of Milan, was preparing to
remove him by force or for some design of his own. Whether this is mere
rashness on Ridolfo's part or something larger is not yet clear. The
Pope's legate has orders to stop him, by force if necessary, and troops
have moved into Parma. Vederassi il successo: we shall see how it
goes.39
Morone's surviving reports independently confirm a public presentation of
papal aid at Speyer on 23 March and complaints that the offer was too small.
They corroborate the decipherment's account, although the particular
enclosed extract has not been identified.40 The Pope and the Emperor
had met at Lucca in September 1541, two weeks after the Turks took
Buda.41
The Gonzaga genealogy also fits. Gianfrancesco's sons included Massimiliano,
who held Luzzara, and Rodolfo, spelled Ridolfo in the letter, associated
with Poviglio in the Parma territory. A published archival inventory
describes a 1546 letter to Rodolfo as "signore di Poviglio". That supports
the proposed castle name without supplying its missing letters.30
The peace Montepulciano was carrying did not come. Francis I declared war on
Charles V in July 1542. By the end of that month Montepulciano was back in
Italy. On 30 July the nuncio Girolamo Verallo reported Ferdinand's statement
that la pratica della pace era exclusa: the negotiation for peace was
finished.42
Status of the decipherment
This is a candidate reading. The key is stable: either half of the letter
alone yields the same letters and null. The page check examined the disputed
readings and the classifier's suspects, not every glyph.
No other cryptanalyst has yet verified or challenged the solution. On
15 September I sent the key and plaintext to MysteryTwister, whose team
checks Level X solutions by hand.7
Sources and research materials
The notes identify the evidence for individual claims, including the
article's own computations and proposed readings. References to printed
books use their printed page numbers; manuscript references use folios.
Cipher-line numbers count only lines containing cipher. English translations
follow the cited Italian passages. The edition supplies word division,
punctuation, and some spelling; its brackets and alignment record uncertain
readings. Online catalog and challenge statuses were checked on
16 September 2026.
Manuscript and transcription

Archivio Apostolico Vaticano (AAV), Segr. Stato, Spagna 1A,
ff. 70r–73v. Letter identified here as Alessandro Farnese to Giovanni
Poggio, Rome, April 1542; day unresolved.
DECODE record 92,
identifier ASV/i1025/SdS/Spain/IA/2. Older references use ASV,
Archivio Segreto Vaticano. The April date is the reading of this letter's
dateline, rather than the wider date range assigned to the archival bundle.
EHum. Transcription of ASV_i1025_SdS_Spain_IA-2, 9 January 2016.
Public original;
complete transcription, including the transcriber's header;
ciphertext appendix and notation. This is the input to
the key search. The
manuscript-corrected transcription
is a later research product, used for the edition's final alignment.

Published sources

Borrelli, Luciano, ed. "Biblioteca trentina [parte seconda]."
Studi trentini di scienze storiche, Sezione prima, 68, no. 2 (1989):
185–214. Digitized article.
Cardauns, Ludwig, ed. Berichte vom Regensburger und Speierer
Reichstag 1541, 1542. Nuntiaturen Verallos und Poggios. Sendungen
Farneses und Sfondratos 1541–1544. Nuntiaturberichte aus Deutschland
nebst ergänzenden Aktenstücken, I. Abteilung, vol. 7. Berlin, 1912.
Digitized edition.
Cited below as Cardauns, with document number and printed page.
Cascella Alcaraz, Sara. "Una cifra imperial en Roma (1543)."
Estudios Románicos 34 (2025): 63–73.
doi:10.6018/ER.613381.
Fabbrici, Gabriele. "Geografia politica della pianura reggiana fra
XVI e XVII secolo. Note introduttive." In Corti e diplomazia
nell'Europa del Seicento: Correggio e Ottavio Bolognesi (1580–1646),
edited by Blythe Alice Raviola, 51–66. Mantova: Universitas Studiorum, 2014. Cited page 61.
Gairdner, James, and R. H. Brodie, eds. Letters and Papers,
Foreign and Domestic, of the Reign of Henry VIII. Vol. XVII, 1542.
London: Her Majesty's Stationery Office, 1900.
British History Online, pp. 286–300.
Gayangos, Pascual de, ed. Calendar of State Papers, Spain.
Vol. 6, part 2, 1542–1543. London: Her Majesty's Stationery Office, 1895. British History Online, pp. 1–13.
Lämmer, Hugo, ed. Monumenta Vaticana historiam ecclesiasticam
saeculi XVI illustrantia: ex tabulariis Sanctae Sedis apostolicae
secretis. Freiburg im Breisgau: Herder, 1861.
Digitized edition.
Lasry, George. "The Vatican Challenge — Part 5." MysteryTwister,
7 July 2019.
Challenge page;
challenge PDF.
Lasry, George, Beáta Megyesi, and Nils Kopal. "Deciphering papal
ciphers from the 16th to the 18th Century." Cryptologia 45, no. 6
(2021): 479–540. First published online 23 June 2020.
doi:10.1080/01611194.2020.1755915.
Litta, Pompeo. "Gonzaga di Mantova," tavola XVI, "Marchesi di
Luzzara estinti nel 1794." In Famiglie celebri di Italia. Milano,
sheet dated 1835. BnF/Gallica, view 26.
Luzio, Alessandro. L'Archivio Gonzaga di Mantova. Vol. II,
La corrispondenza familiare, amministrativa e diplomatica dei Gonzaga.
Verona: Officine grafiche A. Mondadori, 1922.
Digitized edition.
Megyesi, Beáta, Nils Blomqvist, and Eva Pettersson. "The DECODE
Database: Collection of Historical Ciphers and Keys." In Proceedings
of the 2nd International Conference on Historical Cryptology (2019),
69–78. Open proceedings PDF.
Meister, Aloys. Die Geheimschrift im Dienste der päpstlichen Kurie
von ihren Anfängen bis zum Ende des XVI. Jahrhunderts. Paderborn:
Ferdinand Schöningh, 1906.
Digitized edition.
Pastor, Ludwig von. Geschichte der Päpste seit dem Ausgang des
Mittelalters. Vol. V, Paul III. (1534–1549). Freiburg im Breisgau:
Herder, 1909. Digitized edition.
Dates and pages below refer to this 1909 edition.

Individual entries in the Dizionario Biografico degli Italiani are cited
by their named authors, volumes, years, and online entry titles in the notes.
Their online text does not supply printed page breaks. Methodological
references and the signed institutional history of Buda are likewise given
in full at the relevant notes.
Research data and illustrations
The edition appendices contain the key tables,
machine-readable key,
edited Italian text, and
digit-by-digit alignment. The
automatic reading preserves the decoder's proposals,
including those rejected in the edition. The
transcription appendix includes the public and
corrected texts and the individual manuscript decisions. The
results supplement reports the search
and control results, model details, and independent rereadings. The
earlier alignment supplies the before-check
figures in table 5. These are the article's research outputs, not an
independently transmitted plaintext.
The figure source register records source images, folios,
crop coordinates, transformations, and figure data. The public previews and the
full-resolution manuscript photographs are different files; the latter were
supplied through DECODE with restricted access and are not reproduced in full
here. The reproduced details and processed glyphs are identified individually
in the register.
Notes

Stefano Andretta, "FARNESE, Alessandro," Dizionario Biografico
degli Italiani (DBI) 45 (1995),
online entry,
opening and the paragraph beginning In questo periodo: born
7 October 1520; appointed to the papal general secretaryship on
1 January 1538, assisted by Marcello Cervini. Giampiero Brunelli,
"POGGIO (Poggi), Giovanni," DBI 85 (2016),
online entry,
records Poggio's appointment as bishop of Tropea on 4 October 1541
and as nuncio to Charles V on 10 October. Both entries accessed
16 September 2026. ↩︎

Farnese to Verallo, Rome, 18 February 1542, Cardauns, no. 96,
pp. 199–201, especially
200–201:
Sono otto giorni che m. Gio. Montepulciano tornò di Spagna.
This places the return about 10 February. The subsequent passage
says the terms will be proposed in France but does not identify
Ricci as the messenger. Gigliola Fragnito, "RICCI, Giovanni,"
DBI 87 (2016),
online entry
(accessed 16 September 2026), gives the next departure as 28 March,
as does Pastor,
V, p. 471 n. 4,
citing Serristori's report of 29 March (Florence, Med. 3264).
Serristori's report itself has not been inspected here. The
edited cleartext on 70r
prints alli XXV del [passato], but the photograph has further
numeral strokes after the V; the
public transcription retains
them as XXV14^-. The numeral may read xxviij (28). The edition's
shortened XXV is not a secure reading and does not establish a
conflict with the published chronology. ↩︎

Meister (1906), section II, no. 2,
pp. 176–177.
The printed heading reads [Zwischen 1538 und 1542.] Cifra ultima con
Mons. Poggio mandata per il Montepulciano. The date is Meister's
editorial dating. He gives the collection's manuscript source as
"Rom, Bibl. Chigi M II 49 f. 85–148 und f. 168" on p. 176;
this is the source of the comparative keys, not of the letter. ↩︎

AAV, Segr. Stato, Spagna 1A, ff. 70r–73v, DECODE 92.
Compare the public transcription
with the edition's 70r,
72v, and
73v. The phrase about the Ancona
news is freschi et di bon loco. The edited cleartext contains
supplements and omissions; it is not a diplomatic transcription. ↩︎

Cardauns, pp. 437–441: the archival citation "Rom A. V. Spagna
vol. 1 A f. 52–54 Or." is on
p. 437 n. 2.
On p. 439
he states that he selects passages concerning German affairs from
the fragmentarily surviving correspondence of 1542. This selection
does not include the April letter. Its omission does not establish
that he attempted to decipher these leaves. ↩︎

Lasry, Megyesi, and Kopal (2021; online 2020), §5.5, pp. 501–502.
Their comparison with Meister 176/2 concerns IA-1. On p. 502 they
write: "The ciphertexts in the second part (IA-2) seem to belong to
another key." Table 3, p. 496, places Segr. Stato Spagna-1A in
cluster 16; that result concerns the collection, rather than this
letter's digit counts alone. ↩︎

Lasry (2019), challenge PDF,
pp. 4–5,
for the unknown key and plaintext and the tentative language
identification. The
live challenge page
gives the publication date as 7 July 2019 and displayed "0 solves"
when checked on 16 September 2026. This is the site's recorded
status. The author submitted the present result on 15 September;
external verification was pending on 16 September. ↩︎ ↩︎

EHum's transcription header records
eight times totaling 393 minutes (6 h 33 min). Megyesi, Blomqvist, and
Pettersson (2019), §4.1,
p. 73, explain
that the date field records submission and that working time excludes
breaks and quality checks. The transcription appendix
records the counts: 113 cipher lines, 6,577
digit-position tokens, 44 unreadable tokens, and 207 above-marked
tokens (178 dots, 25 commas, four dashes). DECODE's separate
record-creation date, 18 October 2016, is not the transcription date. ↩︎

Author's calculations from the public transcription. The
counting rules and figure data
specify overlapping windows, treatment of unreadable positions and
alternative readings, and the joining of cipher lines and folios
across intervening cleartext. There are 6,492 readable two-position
windows. Digit percentages use all 6,577 positions as their
denominator. The expectation for 00 is an independence comparison
using the observed frequency of 0, not a fitted model of the cipher.
After the 220 occurrences of 73, the next token is 6, 8, 4,
or 5 in 204 cases (92.7 percent); one next token is unreadable. ↩︎

Meister (1906), no. 1,
p. 176,
for single-digit polyphones; no. 2,
p. 177,
for syllables such as ca ce ci co = 21 22 23 24; and no. 4,
pp. 177–178, the 1545 Mignanello key, for vowels 11 13 15 17 19
and single-digit consonant codes, most with two possible readings.
These features can coexist in a key. No. 7, p. 179 (figure 4),
supplies the comparison with a mixed-length monoalphabetic design. ↩︎

The exploratory-search summary
describes the structure tests, unsuccessful searches, and
Mignanello-type vowel-pair test. These used several predecessor
implementations. Their negative results
describe the searches made, not an exhaustive exclusion of those designs. ↩︎

Lasry, Megyesi, and Kopal, §6.10, pp. 522–524, already
describe probabilistic variable-length decoding with Italian
five-grams, logarithmic scores, and spelling normalization, explicitly
for a cipher "for which the key is known" (p. 522). Here the outer
search also changes the unknown key. ↩︎

The corpus account
identifies Machiavelli's Il Principe, Lettere, Discorsi sopra la
prima Deca di Tito Livio, and Istorie fiorentine; Castiglione's
Il libro del Cortegiano; and Vasari's Vite (1550).
The complete corpus contains 4,954,638 normalized letters, including
729,754 from Cardauns; withholding 200 rows leaves 4,899,793 training
letters, including 721,950 from Cardauns. A language heuristic selects
Italian-looking lines, rather than identifying each letter's author.
The Wikisource metadata does not establish the underlying
print edition for every work. The
corpus audit
records metadata contamination, duplicate literary text, and sixteen
held-out rows also present in training; this is not a deduplicated
or independently held-out corpus. ↩︎

Normalization also folds j/y to i, k to c, w to u, and
x to s.
The language model blends
each context's observed distribution with shorter-context estimates,
using weight total/(total + distinct_next_symbols); the base is
uniform. Unspaced training removes
word spaces, retaining beginning/end-of-row sentinels.
The C solver uses a dense table of 3,200,000 float32 base-10 log
probabilities. ↩︎

The search account specifies the beam
decoder, input preparation, and annealing settings. The tightened
search used the unspaced model, no word units, 500,000 proposal attempts,
three restarts, and random seed 11. The candidate-code threshold is
applied to the scored fragments. Invalid proposals are skipped but
still advance the cooling schedule. Above-comma tokens are treated as dotted for
these cuts; the four above-dashes do not trigger cuts. ↩︎ ↩︎

S. Kirkpatrick, C. D. Gelatt Jr., and M. P. Vecchi, "Optimization by
Simulated Annealing," Science 220, no. 4598 (1983): 671–680,
especially pp. 672–673,
doi:10.1126/science.220.4598.671
(scan).
This is the general method. Table 1 summarizes the cipher-specific
settings; the search account gives
the move probabilities and cooling schedule: swaps, 45%; moves to
unused codes, 45%; deactivation of optional units, 10%. A worse key
is accepted with probability exp(Δ/T), where Δ is the change
in total score and T falls geometrically from 30 toward 0.5. ↩︎

The search results
include the first successful run, which produced the quoted opening
and the common eighteen-letter key in restarts 0, 3, 4, and 5,
alongside the three-null, homophone, and tightened searches.
These are exploratory runs with changing
model inventories, rather than a controlled language-performance test. ↩︎

The retained-digit count includes 26 digits in fragments
shorter than three, which the decoder does not score. The scored
fragments contain 6,305 digits. The whole-letter scores divide by
6,331, matching the saved runs. ↩︎

The control results report
both halves at seeds 11 and 23, the clean and noisy synthetic ciphers,
and the shuffled ciphertext. The clean and noisy
cases use different invented keys. Retained-digit denominators are
2,591 and 3,740 for the halves, 6,165 and 6,119 for the synthetic
cases, and 6,331 for the shuffle. Deterministic reruns reproduced
the recorded keys and scores. Training overlap is documented in
the corpus account cited above. ↩︎

Lasry, Megyesi, and Kopal, §5.3, p. 498: "In this
project, the recovery of keys for variable-length homophones could
only be achieved from matching plaintexts or by finding the key in
the sources (e.g., Meister), based on characteristics identified via
statistical analysis." The authors also report plaintext-assisted
recovery of variable-length monoalphabetic examples F6 and P1
(pp. 499, 501). Their account does not establish a general limit on
ciphertext-only recovery or priority for the present result. ↩︎

Recovered key, regular codes
and dotted codes, with contextual
examples; machine-readable key.
These assignments are the article's reconstruction. The
unresolved marks
include dotted signs whose meanings remain unknown. The
edition's alignment records the use of
each assignment, including nulls, and the departures needed at
individual occurrences. ↩︎

The exact sequence occurs on f. 70v twice and f. 71r twice;
line and token locators.
See the edition's reading note
and the saved automatic reading, which
preserves the rejected santa readings. The choice between santa
and spesa is contextual: both segmentations use the same key
without changing a digit. ↩︎

Costs for a digit and its mark add together; candidate-code matches
costing more than 6.5 are rejected. Paths reaching the same digit
position with the same four-letter context are merged, and the decoder
keeps up to 64 contexts before advancing. It records the steps needed
to trace the winning reading back to its digits. A literal null carries
the context through unchanged at no cost; a title code resets the
context without spelling its abbreviation into the language model.
The automatic reading records the fixed-key
decoder's results under the edit costs in table 3, with source digits
above decoded units and changed units marked. Its folio 70r
edit list includes the Montepulciano substitution; folio 71r
includes the rejected galley reading. Its final tally has 165 edited units
containing 170 operations: 44 fills and 126 other operations;
126/6577 = 1.916%. An operation count is not a measured
transcription-error rate, and rejected proposals remain in this output. ↩︎ ↩︎

Editorial conventions and
alignment notation.
The alignment procedure finds a least-cost alignment of an already
supplied edited text.
Bracketed supplied letters receive a reduced cost, and gaps can
absorb digits without cost. Its alignment therefore records how
the edition can account for the digits; it is not an independent
test of the edition's correctness. ↩︎

The rereading supplement includes
the 72r and 71v input packets and responses and describes the
adopted corrections. Both successful
readers were fresh GPT-6 Astra runs. Their packets shared the
language-model-selected strict segmentation as well as the key and
transcription, omitted unreadable tokens and short fragments, and
used the first listed alternative readings. They did not contain
manuscript images or the edition.
Thus their independence is limited to the subsequent reading task. ↩︎

The pilot account
describes four strips totaling 55 reference digits and runs of
grok-4.6, gpt-6-astra, and gemini-3.1-pro at #high.
The scoring allowed fractional alternatives and free crop-edge
extras; its reference largely followed the public transcription.
Prompts, responses, and the restricted-image crops
are not included. This account supports a reported pilot,
not a reproducible comparative benchmark. ↩︎

The glyph-classification account
describes line leveling, slant removal, cuts, and token-to-ink alignment.
Neighbor selection excludes references from the current line. The
evaluation gives 90.549% agreement on 6,497 labeled glyphs and 98.885% on
4,485 glyphs with vote share at least 0.9 (69.03% of the set).
PCA and segmentation use the full dataset; line exclusion applies
to the neighbor lookup. These are agreement rates against
provisional transcription labels. Figure 9's
processing record specifies
the features, distances, and source glyphs. ↩︎

Manuscript-check account,
individual decisions,
correction ledger, and
dot decisions. All 196 classifier
suspects have entries in the decision ledger. Applying sure or
probable corrections at the original transcription's positions produces the
corrected transcription. ↩︎

The correction ledger identifies
each change by folio, cipher line, and original token position.
The five doubled groups are 71v L04 p30–34, L05 p21–23,
L09 p46–51, L20 p42–45, and 72r L07 p27–29: lengths
5 + 3 + 6 + 4 + 3 = 21. There are fourteen inserted digits and
29 deletions overall, giving 6577 − 29 + 14 = 6562.
The manuscript-check account
discusses the individual readings, including the two swapped pairs and
the Emperor's title on 72r; the
dot ledger records risposta
at 70v L05 p26–27 and Marchese at 73r L01 p57–58.
The duplicated-digit count is the sum of the correction rows. ↩︎ ↩︎

Litta, "Gonzaga di Mantova,"
tavola XVI,
entries Gianfrancesco, Massimiliano, and Rodolfo, connects
both sons to Gianfrancesco and Laura Pallavicino. Their entries
discuss the dispute over Luzzara and associate Rodolfo with the
castello di Poviglio nel parmigiano. The sheet reads Stampata
nel 1835; the BnF copy is NE-49 (A)-FOL, Gallica view 26 of 34.
Fabbrici (2014), p. 61, also identifies Massimiliano as
Gianfrancesco's son and successor at Luzzara. Borrelli (1989),
p. 195, no. 592,
describes a letter of Leoncino to "Rodolfo Gonzaga, signore di
Poviglio," Mantua, 15 February 1546, with capitulations for the sale
of Poviglio to Nicolò d'Arco: Guastalla, Biblioteca Maldottiana,
Fondo Davolio Marani, 12 n. 72. This is the published inventory's
description; the underlying manuscript has not been inspected here.
Luzio (1922), p. 262,
places Poviglio among the Gonzaga possessions in the Parmense.
These sources support the contextual identification, not the absent
letters in P[o]ui[glio]. ↩︎ ↩︎

The bracket check has a known omission: on 71r the u in
sua parte, "his share", is unbracketed although it needs
1 and the corrected transcription offers 3/7. The alignment lists
3/7>1, but wrongly treats it as a choice between recorded alternatives. ↩︎

The "before" column describes the pre-manuscript-check edition
against the public transcription, preserved in the
earlier alignment, final totals:
5847 + 369 = 6216 exact tokens and nulls;
260 + 18 + 22 = 300 tokens in edited units, read as nulls, or dropped.
The "after" column uses the revised edition and corrected digits,
current alignment, final totals:
5993 + 365 = 6358 exact tokens and nulls;
154 + 10 + 6 = 170 tokens in the departure categories.
Both tokens of an edited pair enter that category even if only
one was altered. Supplied letters consume no source tokens and
therefore do not increase these counts. ↩︎

Marco Grilli, Segretario della Prefettura, Archivio Apostolico Vaticano,
email to the author, 16 September 2026; private correspondence.
The report concerns index 1017 for Segr. Stato, Principi 14A, the
register Cardauns cited as Principi 14. It does
not report a folio-by-folio examination of the register and does not
establish that no copy survives. The email itself is not reproduced here. ↩︎

AAV, Spagna 1A, ff. 70r–70v; edited decipherment,
70r and
70v, from Dopo la partita to
secondo che V.S. scri[u]e per le sue. The letter says a copy of
Doria's written summary accompanies it; that enclosure has not been
identified here.
For Aguilar's identification as Juan Fernández Manrique de Lara y
Pimentel and his Roman embassy, see Cascella Alcaraz (2025), pp. 63–64.
For Andrea Doria's imperial naval command, Edoardo Grendi,
"DORIA, Andrea," DBI 41 (1992),
online entry,
the 1528 asiento paragraph (accessed 16 September 2026). ↩︎

AAV, Spagna 1A, ff. 70v–71r; edition, 70v,
acciò che non si cadesse in questo errore di spender in vano in un
luogo che manco lo ricercasse, et non poter di poi supplir a l'altro
dove fusse maggior il pericolo. The English quotation translates
this passage. ↩︎

AAV, Spagna 1A, f. 71r; edition,
armar le cento navi through sua parte che [l]i toccherà.
The judgment about mixed fleets is the Pope's argument as reported
in the letter. Navi is rendered as sailing ships in contrast to
galere; the six galleys are explicit in the decipherment. ↩︎

AAV, Spagna 1A, ff. 71r–71v; edition, 71r,
Ma quanto a le fanterie, continuing on
71v to per la difesa dal Turco. ↩︎

AAV, Spagna 1A, ff. 71v–72r; edition, 71v,
tra le quali è lo aiuto di Ungaria, continuing on
72r. The corrected reading
la S.M.tà [h]a voluto attributes the request for a public offer
to the Emperor. The enclosed capitulo has not been identified as a
separate witness. Speyer is named in the cleartext on
73r, della [dieta] di Spira.
Massimo Firpo, "MORONE, Giovanni," DBI 77 (2012),
online entry
(accessed 16 September 2026), confirms his bishopric and attendance
at Speyer in 1542. Granvelle here is Nicolas Perrenot: Gayangos
(1895), no. 2, pp. 2–7, especially
p. 3 and its identifying note,
and no. 6, pp. 10–11, addressed to him as the Emperor's
Garde-sceaux. ↩︎

AAV, Spagna 1A, ff. 72v–73r; edition, 72v,
Il Signor Ridolfo Go[n]zaga, continuing on
73r to Vederassi il successo.
The unidentified employer and conjectural castle name remain open;
this summary does not independently establish the troop movements.
For the identification of the Marchese del Vasto as Alfonso d'Avalos,
governor of Milan from 1538, see Gaspare De Caro, "AVALOS, Alfonso d',
marchese del Vasto," DBI 4 (1962),
online entry,
the paragraph beginning Alla morte del Caracciolo (accessed
16 September 2026). ↩︎

Morone to Farnese, Speyer, Lämmer, no. CCXXXVIII, pp. 419–423,
especially p. 420:
Alli XXIII. hebbi audientia publica and esposi la mente di N. S.
sopra l'aiuto contra il Turcho. The response acknowledges his
proposal in the Pope's name. Lämmer's heading dates the report
28 March; Cardauns, p. 127 n. 1, refers to it as 29 March. The
presentation's date, 23 March, is explicit in the text.
Morone's report of 30 March, Cardauns, no. 63, pp. 127–130, at
128, lines 6–17,
says Quanto al aiuto contra il Turcho tutti si aggravano parendoli
poco; the majority wanted 5,000 infantry without conditions and
2,000 cavalry. These passages establish the presentation and
dissatisfaction, not Charles V's personal instruction or the
identity of the letter's enclosure. Earlier discussions with the
Emperor at Lucca and then Granvelle are attested in Farnese to
Verallo, 7/10 January 1542, Cardauns, no. 93, pp. 192–195, at
193.
That passage does not independently establish the precise Roman
settlement described in the decipherment. ↩︎

Pastor, V (1909), pp. 456–458, especially
457:
Charles V arrived and met Paul III on 12 September 1541; extended
discussions began the next day. Károly Magyar, "Buda in the Turkish
Era," The Castle of Buda, signed institutional account credited
to the Budapest History Museum and HAS Research Centre for the
Humanities, part 1, final paragraph
(accessed 16 September 2026), dates the Ottoman occupation to
29 August. The interval to their first meeting was fourteen days. ↩︎

Gairdner and Brodie (1900), p. 287,
no. 492, "The War",
calendars Francis I's proclamation against the Emperor, dated
Ligny, 12 July 1542, from a copy at Simancas. For Ricci's return to
Rome on 22 July, see Fragnito, "Ricci," and Pastor, V,
p. 472.
The quotation is in Verallo to Farnese, Nuremberg, 29/30 July,
Cardauns, no. 112, pp. 229–233, at
231, the 30 July continuation:
la Mtà del re mi ha communicato that Montepulciano had returned
and la pratica della pace era exclusa. Verallo is reporting
Ferdinand's account. Ricci's mission had failed; papal mediation
continued, with new peace legates appointed on 7 August (Pastor,
p. 472). ↩︎

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The analysis of the Farnese letter, written in April 1542, involves the process of deciphering a complex cipher embedded within the text, which originated from Cardinal Alessandro Farnese, grandson of Paul III, to Giovanni Poggio, the Pope's ambassador. The cipher is characterized by digits interspersed within the prose, presenting inherent ambiguity where sequences of digits can correspond to multiple letter combinations, even with a known key. The initial difficulty lies in determining the segmentation of the digits, making the task of finding the correct key and plaintext highly complex.

The cryptanalytic effort employed sophisticated methods, including digit-frequency analysis and the application of a five-gram language model trained on historical Italian texts such as those by Machiavelli, Castiglione, and Vasari, to estimate the probability of letter sequences. The process involved an outer search to test potential plaintext assignments and an inner decoder utilizing a beam search algorithm to navigate the vast space of possible digit groupings. This decoding process incorporated edit costs, allowing the system to evaluate the trade-off between maximizing the probability of the reading and minimizing modifications made to the transcribed text. The overall methodology relied on simulated annealing to explore the solution space, allowing the search to accept suboptimal moves to escape local optima.

The process culminated in the recovery of a stable key, which was verified using control runs involving synthetic ciphers and shuffled ciphertext. The recovered key, along with the contextual elements, was further refined by examining the meaning of dotted codes and inconsistencies in the transcription. The statistical analysis revealed patterns where certain digit pairs corresponded to common letter combinations, and the language model helped resolve ambiguities, such as distinguishing between related concepts like "la santa" (the holy enterprise) and "la spesa" (the expense) based on the surrounding argumentation.

Following the key recovery, further work focused on reconciling the deciphered text with the manuscript photographs. This involved a specialized classifier that compared the transcribed glyphs (such as the name of Montepulciano) against visual evidence from the manuscript. This system was used to identify transcription errors, recognizing how scribal habits, such as joining digits, altered the appearance of the original writing. Detailed procedures were established to trace specific changes, allowing for the reconstruction of the original text while explicitly marking conjectural readings and accounting for the discrepancies found between the transcription and the manuscript image.

The final deciphered content reveals the diplomatic negotiations surrounding the peace between the Emperor and France, noting Emperor Charles V's concerns regarding the funding of a hundred ships and the possibility of neutrality for the Pope to broker peace. It details the status of the Hungarian subsidy, which was being offered publicly at the Diet of Speyer, and discusses the actions of Ridolfo Gonzaga regarding territorial holdings in Parma. The process of decipherment thus provided not only a textual translation but also offered a critical examination of the source materials, establishing a chain of evidence linking the cipher to historical political and familial events.