Manzoni's plague: Milan 1630 through the eyes of an OSINT analyst

In chapter XXXI of The Betrothed (I promessi sposi), after describing how Milan refused for weeks to call the plague by its name, Alessandro Manzoni pauses and writes a sentence that, as an analyst, I consider one of the best definitions of method ever written:

Si potrebbe però, tanto nelle cose piccole, come nelle grandi, evitare, in gran parte, quel corso così lungo e così storto, prendendo il metodo proposto da tanto tempo, d'osservare, ascoltare, paragonare, pensare, prima di parlare.

"In small things as in great, that long and crooked course could largely be avoided by adopting the method proposed so long ago: to observe, listen, compare and think, before speaking."

Observe, listen, compare, think, before speaking. In five verbs, that is the work of anyone doing open-source analysis, what we now call OSINT (Open Source Intelligence). In recent days I applied this method to a current case, the suspected plague in Irkutsk, and before that to the Black Death of the fourteenth century. Here I go the other way: back to the plague told by Manzoni, read as I would read a case file.

You will find that Milan, in 1630, went through almost every information failure we still see today: denial, softened words, uncontrolled rumours, rewards for denunciations, extracted confessions. And that Manzoni, two centuries later, took them apart one by one with an analyst's method.

The sources: who tells the story of the 1630 plague

Every analysis begins with an inventory of sources. For the Milan plague, the main ones are three contemporary accounts that Manzoni knew well and used openly.

The first point to note is that none of these sources is neutral. A Health Tribunal physician has an interest in showing the Tribunal was right; an archbishop reads events through faith; a historian writes to leave a work behind. This is where every analyst starts: there are no sources without a point of view, only sources whose point of view is known.

First exercise: patient zero

Take Milan's first patient, what we would now call "patient zero". The two main sources disagree (Italian Wikipedia):

The name is almost the same, the date differs by exactly one month, the origin does not match. Faced with a table like this, an analyst asks three questions: is it the same person? Did one copy the other badly, or did they draw on different sources? Which of the two had direct access to the documents?

Manzoni does something few popular writers do even today: he records the discrepancy instead of choosing one version and staying silent about the other. He leaves the reader the raw data and the doubt. It is the first principle of source analysis: when two witnesses disagree, the disagreement is itself information, and erasing it for a cleaner story means falsifying it.

Second exercise: how to deny reality with words

The Landsknechts, imperial troops heading to the siege of Mantua during the succession war, crossed the Valtellina and Lombardy from autumn 1629, bringing the disease with them. The Health Tribunal had feared exactly this. But when the illness began to appear in Milan, part of the authorities and the population reacted by denying it.

Manzoni describes this denial in a famous passage, worth reading in full:

In principio dunque, non peste, assolutamente no, per nessun conto: proibito anche di proferire il vocabolo. Poi, febbri pestilenziali: l'idea s'ammette per isbieco in un aggettivo. Poi, non vera peste, vale a dire peste sì, ma in un certo senso; non peste proprio, ma una cosa alla quale non si sa trovare un altro nome. Finalmente, peste senza dubbio, e senza contrasto: ma già ci s'è attaccata un'altra idea, l'idea del venefizio e del malefizio, la quale altera e confonde l'idea espressa dalla parola che non si può più mandare indietro.

"At first, then, not plague, absolutely not, on no account: even uttering the word was forbidden. Then, pestilential fevers: the idea is admitted sideways, in an adjective. Then, not true plague, that is to say plague yes, but in a certain sense; not plague exactly, but something for which no other name can be found. Finally, plague beyond doubt and beyond dispute: but by now another idea has attached itself, the idea of poisoning and sorcery, which alters and confuses the idea expressed by the word that can no longer be taken back."

It is a lesson in language analysis. Manzoni identifies four stages:

1. Total denial. The word is forbidden.
2. The adjective. Reality slips in sideways, softened: "pestilential fevers".
3. The circumlocution. The thing is admitted, but not the name.
4. Contamination. When the word is finally accepted, it is already loaded with another idea: conspiracy.

Anyone who works with open sources recognises this pattern everywhere. In recent days we saw it in the Irkutsk case, where Russian authorities spoke for days of "pneumonia of unknown aetiology". I am not saying there was plague in Irkutsk: we do not know. I am saying that the choice of words is data to be analysed, not a detail. When an institution systematically avoids a word, that choice should be recorded, together with the facts that contradict or confirm it.

There is a human side too. Ludovico Settala, Milan's most authoritative physician, was accused by part of the population of leading those who spread news of the disease (Avvenire, in Italian). Whoever brings unwelcome news always risks being treated as the cause of the problem.

Third exercise: the event that amplifies the contagion

In June 1630, with the epidemic already under way, the city asked for a great procession with the relics of Saint Charles Borromeo. Cardinal Federico Borromeo was reluctant, then agreed. The procession, with an enormous crowd, coincided with a rise in contagion (Avvenire).

A methodological caution is needed here. For an analyst, "coincided with" does not equal "caused". But a gathering of thousands of people during a contagious epidemic is exactly the kind of event one expects to see followed by a peak. It is a strong hypothesis, consistent with what we know today about disease transmission and with what contemporaries observed.

What is interesting is that today we can begin to test it with data. In 2023 a research team from the University of Milan, led by Massimo Galli and Francesco Comandatore, digitised the 1630 Milan death registers and published their analysis in the journal iScience. One finding is that the epidemic did not develop the same way across the city: the parishes fall into two groups with different epidemic curves, possibly for social or demographic reasons (University of Milan).

This is OSINT applied to history: taking a public but forgotten source, a register of the dead, turning it into data and letting it tell what the chronicles do not.

Fourth exercise: the rumour that becomes a trial

The anointings

On the night of 17 May 1630, traces of an oily substance were found on some benches in Milan Cathedral. More were found the next day. On 19 May a grida, a public ordinance, denounced those responsible and promised rewards to anyone who exposed them. Further gride, on 13 June and 7 August, raised the rewards and the penalties (Italian Wikipedia).

Pause on this detail, because from an analytical point of view it is the most important: the authorities paid for denunciations. In a climate of panic, a reward for reporting an "anointer" does not produce better information: it produces more reports, and less verified ones. It is a mechanism we know well today, whenever visibility or money rewards whoever spreads a story first rather than whoever verifies it.

The case of Guglielmo Piazza and Gian Giacomo Mora

On the morning of 21 June 1630, along the Corso di Porta Ticinese, oily stains were noticed on some walls. A woman, Caterina Rosa, accused a man she had seen passing: it was Guglielmo Piazza, a health commissioner, who was there for work.

Piazza was arrested and tortured. Under torture, and with the promise of immunity, he ended up accusing a local barber, Gian Giacomo Mora, of supplying him with the ointment. Mora, also tortured, confessed. Both were convicted and executed on the wheel. Before dying, both declared their innocence (Italian Wikipedia).

Mora's house and shop were razed. On the ruins a column was erected, the column of infamy, with a Latin plaque recording the sentence. It stood for almost a century and a half: it was torn down on the night of 24–25 August 1778. The plaque is now kept at the Castello Sforzesco, and in 1868 the street was named after Gian Giacomo Mora himself (MilanoFree, in Italian).

What an analyst sees in this trial

Reread today, the Piazza–Mora trial is a catalogue of methodological errors:

• A single, unverified testimony, taken as a certain starting point;
• an interpretation in place of a fact: Caterina Rosa saw a man passing close to the walls, not anointing anything;
• confession as the queen of evidence, obtained through torture, a method that produces the answers the interrogator wants to hear;
• chain confirmation: Piazza's confession "proves" Mora's guilt, and Mora's confirms Piazza's, without either element ever being independently verified;
• no corpus delicti: nobody ever showed that the ointment could transmit plague.

It is the same pattern I described regarding Anne Boleyn: a verdict already written, and evidence built to reach it.

Manzoni against the "spirit of the age"

Manzoni devoted an entire work to this trial, The Column of Infamy (Storia della colonna infame), published in 1840 as an appendix to the definitive edition of The Betrothed.

Before him, in the eighteenth century, Pietro Verri had already used the case in his Observations on Torture to show the absurdity of judicial torture. Manzoni, a grandson on his mother's side of Cesare Beccaria, author of On Crimes and Punishments, went a step further. He rejected the most convenient excuse, that the judges were "children of their time" and could not have done otherwise. His most famous sentence on this point is a principle that holds for every investigation:

L'ignoranza in fisica può produrre degl'inconvenienti, ma non delle iniquità; e una cattiva istituzione non s'applica da sé.

"Ignorance of physics may cause mishaps, but not iniquities; and a bad institution does not apply itself."

In today's language: not knowing how a disease spreads was a limit of the age, and nobody can blame the judges for it. But torturing, ignoring contradictions, convicting without evidence were choices. Wrong tools do not use themselves: someone decides to use them.

Renzo, the anointer who wasn't

There is a moment in The Betrothed that makes all this concrete. In chapter XXXIV, Renzo, arriving in a plague-ravaged Milan to look for Lucia, is mistaken for an anointer by an enraged crowd, and saves himself only by jumping onto a cart of corpses driven by the monatti, the plague gravediggers.

Manzoni does not choose this by chance: he puts his protagonist, an innocent the reader knows well, in the same position as Piazza and Mora. For a moment the reader sees from the inside how a misunderstood gesture, a rumour, a frightened crowd are enough to turn anyone into a culprit.

What Manzoni's plague teaches anyone who does OSINT

Lined up, the lessons of Milan in 1630 are the basic rules of my work.

These are the rules I apply every time I carry out an OSINT analysis for a client: building a picture from public sources, documenting the process, and strictly separating what is established from what is hypothesis. And they are the same rules I use in historical research, when an archive, a register or a forgotten chronicle has to be questioned rigorously.

Almost four centuries later, Manzoni's advice remains the best I know: observe, listen, compare, think. And only then, speak.

Works cited: Alessandro Manzoni, I promessi sposi (definitive edition 1840–1842), chapters XXXI–XXXIV, and Storia della colonna infame (1840). Manzoni's works are in the public domain; the English renderings of the quoted passages are my own.