Most of the details of Descartes’ alleged journey to Italy are known only from Baillet’s biography, La vie de Monsieur Des-Cartes (1691, vol. I, pp. 117-28). According to Baillet, Descartes left Paris in September 1623 for a one-and-a-half year trip to Italy, and returned via Lyon in May 1625. Baillet has much to say about where Descartes went and whom he met, but his account could never be confirmed by independent evidence. This is why several historians of philosophy have given it almost no importance, while others believe that this long journey must have marked the philosopher’s life and career. That Descartes actually went to Italy is clearly indicated by his letters; what is sorely lacking, however, is definite information about the places he visited or the people he met. All we know from the correspondence is that he did not like the climate or the food in Italy. [*]
I have recently found evidence that casts light on Descartes’ journey to Italy. It compels us to reduce his journey to only six weeks, from the end of March 1625, when he left Paris, to the beginning of May 1625, when he arrived in Lyon. The historical documents found are an inventory after his death and a deed drawn up before a notary in Lyon, both dating from 1625. The crucial passages of the first document [A] are discussed below, and the full text of the second document [B] is given in the appendix. We will first discuss what motivated this travel project; then what the new documents tell us about it; finally we will try to reconstruct the way Baillet misinterpreted the journey, by briefly recalling what Descartes certainly did not do in Italy.
According to Baillet, the reason for Descartes’ trip to Italy was the death, in Turin, of a relative who had accompanied the French expeditionary army to Piedmont as Commissaire général des vivres, a very important position. This relative would be a certain M. Sain, husband of Descartes’ godmother, who died in early March 1623 (Vie, I, 118). Baillet then summarizes a letter from Descartes to his elder brother Pierre, dated March 21, 1623, according to which he is going to settle the affairs of the deceased and see if he can acquire his office; all the necessary arrangements for the trip would have been made and he would like to leave for Turin the next day (AT I, 3). However, according to Baillet, instead of leaving the next day, Descartes would have gone to Poitou to sell some goods, would have returned to Paris in the summer and would have begun his journey in September.
In reality, Baillet’s account cannot be entirely correct. First of all, he is mistaken about the identity of the relative, for Jean Sain, the husband of Descartes’ godmother, had already died in 1619. The relative referred to here is René Sain, first cousin of Descartes’ mother, Jeanne Brochard. The second error is that René Sain did not die in 1623, but in 1625.
René Sain, sieur de Rochefort, married Léonore de Féal (or Foyal) in 1603. The couple had seven children, the oldest of whom was also named René, like his father. One of the daughters, Françoise, married Guillaume du Tronchay, sieur de Martigny, in February 1624; Descartes knew him personally, and he rendered some services to Descartes in Paris from late 1639. In March 1622, René, the father, was appointed Conseiller secretaire du Roy et Grand Audiencier de France, a position from which he resigned in September 1624, presumably in preparation for his appointment as “superintendent of supplies to the camps and armies, munitions and stores of France” in the impending French military campaign against the Spanish-backed Republic of Genoa. The French army led by the Duke of Lesdiguières, Constable of France, arrived in Turin in February 1625. René Sain died in Turin on March 3, 1625 — the date of his death, the place and his office as “superintendent of supplies” are mentioned in the inventory after death drawn up at the request of his widow in Paris on April 3, 1625.
Descartes is mentioned in an addition to the inventory :
Du vendredy vingt troise jour de may audict an  fut faict et inventorié ce qui s’ensuict. Ensuyvent les papiers et enseignemens qui estoient où ledict deffunct Sr Sain est decede et qui onct esté raportéz à ladicte présente. […] Item trois pièces attachées ensemble. La première est une promesse du Sr de Thorigny dactée du xiiie avril mvic vingt cinq contenant ledict Sr debvoir au Sr Descartes la somme de sept cens vingt livres pour la vente des mullectz que appartenoient audict deffunct Sr Sain. La seconde est une lettre de change de ladicte somme tirée par ledict Sr de Thorigny le mesme jour et an sur le Sr Vuidaud l’Aisné, marchand à Lion, pour paier ladicte somme audict Sr Descartes, et la troise pièce est un acte de protestation de ladicte lettre de change faicte par ledict Sr Descartes audict Vuidaud pardevant André Dechuyes, notaire audict Lion, en dacte du septe jour de may audict an mvic vingt cinq, partant reffus faict par ledict Vuidaud de paier ladicte somme.
On Friday 23 May 1625 the following was inventoried: Below follow the papers and instructions that were at the place where the late Mr Sain died and which have been reported to his widow who is present. […] Item three pieces attached together. The first one is a promise of Mr de Thorigny dated April 13, 1625, acknowledging his debt to Mr Descartes of 720 pounds for the sale of mules which belonged to the deceased Mr Sain. The second is a bill of exchange of the aforementioned sum drawn by Mr de Thorigny the same day and year on Mr Vuidaud the Elder, merchant in Lyon, to pay the said sum to Mr Descartes. And the third piece is an act of protest of the aforementioned bill of exchange by Mr Descartes to Vuidaud before André Dechuyes, notary in Lyon, dated May 7, 1625, because of the refusal of Mr Vuidaud to pay the aforementioned sum.
The three documents discussed in this text concern a transaction between Thorigny and Descartes, the former buying from the latter several mules that had belonged to the deceased René Sain for 720 livres. Descartes received an acknowledgement of debt and a bill of exchange to be cashed at a certain Vidaud in Lyon. Called upon to honor it, Vidaud refused to pay, hence the act of protest drawn up before the notary, a usual procedure in such cases. The fact that these documents are mentioned in the inventory shows that the debt of 720 livres (a considerable sum) had not yet been settled. The minutes of the act of protest, bearing Descartes’ signature, have been preserved (see below, Appendix B), which proves that the “Sieur Descartes” mentioned in the inventory is indeed René Descartes. In addition, this document reveals Vidaud’s first name — Jean —, Thorigny’s title of nobility — Count — and the place where the transaction took place — in the camp of the French army in siege of the fortified town of Gavi (about 50 km north of Genoa). Jacques Goyon de Matignon (1599–1626), Count of Thorigny, served in the expeditionary army of the Duke of Lesdiguières as “maître de camp” of a light cavalry regiment. The act of protest thus confirms a remark of the old biography of Pierre Borel (1656) according to which Descartes would have visited the seat of Gavi. Baillet knows this biography (Vie, I, 126) and suggests that at Gavi Descartes met Pierre de Boissat (1603–1662; Vie, I, 145), who made his career in the army but was also a man of letters, and in 1634 one of the first members of the French Academy. He actually participated in the campaign against Genoa. He seems to have become an admirer of Descartes’ philosophy, but there is no evidence that the two men met under the walls of Gavi.
Sain’s children were less than 25 years old, so they were still minors: this is why the widow Léonore de Féal had to look for a reliable person “to put the affairs of the deceased in order” (AT I, 3). A cousin with no ties and no fixed position, who also had experience of travel and was familiar with military life, was therefore an ideal candidate for this task. Descartes wrote to his brother that all the necessary arrangements had been made, for example a power of attorney allowing Descartes to act on behalf of the heirs – unfortunately no such document was found in the archives of the notary who drew up the inventory. Of course, Descartes would be well rewarded for his efforts, and he could also let his brother know that “if he did not return richer, at least he would return more capable” (AT I, 3).
The main question is why Baillet believes that Sain died in 1623. We must first note that Baillet is right in asserting that Sain died in Turin at the beginning of March: he must have found this information in Descartes’ letter to his brother. The date of this letter is, according to Baillet, March 21, 1623; but if the day and month are probably correct, the year is certainly not: it must be 1625, since René Sain died on March 3, 1625. This error is probably explained by the fact that Descartes dated his letter “de Paris, ce 3 mars” without specifying the year. From his errors about the identity of “M. Sain” and the date of René Sain’s death, Baillet had to improvise: he conjectured that Descartes had returned to France via Lyon in May 1625, and then assumed that Descartes had gone directly to Poitou to inform M. Sain’s widow, i.e., Jean Sain’s widow, when in fact he had to go first to Paris to see René Sain’s widow, Léonore de Féal. Since the only other documents he had were contracts of sale from June and July 1623, drawn up in Poitiers and Châtellerault (Vie, I, 116), Baillet imagined what might have happened in this gap in Descartes’ biography. From Borel, he knows that Descartes was at the siege of Gavi (April 1625); from Descartes’ papers, he also knows that he had promised to make a pilgrimage to Loreto (cf. AT X, 217-8). Wondering what Descartes might have done in Italy between 1623 and 1625, he had him attend the ceremony of the Wedding of the Sea in Venice (May 1624) and the opening of the Holy Year in Rome in December 1624. Moreover, he assumes that Descartes met powerful princes and cardinals, men of science and philosophers, and he does not hesitate to give their names. Finally, by dating Descartes’ letter to his brother to 1623, he can claim that Descartes was a spectator of the Rosicrucian frenzy, but Didier Kahn has already shown that all that Baillet says about it is unreliable, and that given the plague epidemic, it is unlikely that Descartes was in Paris in August 1623. We can add that for the same reasons it is unlikely that Descartes was in Paris between February and April 1623.
In sum, Descartes’ Italian journey was very short. He left Paris on 22 March 1625, as he told his brother. Once arrived in Turin, he discovered that the army had left the city, and was laying siege to Gavi. Descartes went to Gavi, made the necessary arrangements, including the sale of some mules on 13 April, and he did not acquire the post of army intendant. He returned presumably to Turin, and then headed back through the Alps to Lyon, where his presence is attested on 7 May. Descartes was less than a month on Italian soil, and did not visit Venice, Loreto or Rome. Nor did he, as Baillet wants us also to believe, make a such thorough study of human nature during his travels in Italy, that he saw no need to continue his journey to Sicily and Spain (Vie, I, 122)! What we are left with is a gap in Descartes’ biography from July 1623 to March 1625. It seems likely, though, that Descartes was present at the wedding of his brother Pierre in Elven in September 1624.
Appendix B. Notary deed signed by René Descartes, Lyon, 7 May 1625. Archives départementales du Rhône et de la métropole de Lyon, 3 E 3985, fo. 167r–v (André Dechuyes, notary public).
Photographs of the manuscript are found below.
Du Mercredy vij May 1625. Protest Descartes, de Touriny, Vidaud.
En presence etc. <rayé : noble> René Descartes, escuyer Sr du Perron, a exhibé et presenté au Sr Jean Vidaud l’aisné, marchand demeurant à Lyon, une lettre ou mandat à luy adressante, faicte et signée par Monsieur Le Comte de Thorigny, dattee au Camp devant Gavy le treiziesme Apvril dernier, de la somme de sept centz vingt livres tournoiz payable audict Sr Descartes à lettre veue, et a sommé ledict Sr Vidaud d’accepter ladicte lettre et luy payer ladicte somme qu’il offre recepvoir et faire aquict vallable parlant à la personne dudict Sr Vidaud treuvé audict Lyon, en son domicille, lequel a faict responce, que par faute de provision il ne la peut payer. C’est pourquoy ledict Sr Descartes a protesté de tous despens, dommages et interestz faictz et à faire, et de prendre ladicte somme à change et rechange en ceste dicte ville de Lyon pour tel lieu et pris que bon luy semblera aux frais et despens dudict Sr Comte, et autres qu’il appartiendra, dont a esté faict le present acte audict Lyon, lieu susdict, le septiesme jour du mois de May avant midy mil six centz vingt cinq, presentz Charles Girard, clerc, et Charles Dechuyes, ciergier dudict Lyon, tesmoins requis qui ont signé avec ledict Sr Descartes, non ledict Sr Vidaud de ce requis et sommé.
C. Dechuyes, présent R. Des Cartes
[*] The text published here is the English version of a short note published in the Bulletin cartésien LI (2022), and can be downloaded at the website of Centro dipartimentale di Studi su Descartes “Ettore Lojacono”, University of Salento.
 As I did not visit the Archives nationales de France in Paris nor the Archives départementales du Rhône et de la métropole de Lyon myself, I am very grateful for the help I received from several people. I would like to thank the active contributors of the project Familles Parisiennes (see note 7), Laurence Abensur-Hazan, généalogiste, for finding and photographing the marriage contract mentioned in note 3, Béatrice Beaucourt, genealogist et paleographer, for decyphering passages that were very hard to read in the Lyon notary deed, and finally to the staff of the Arch. dép. du Rhône for their determination to retrieve that particular notary deed.
 An army intendant is a civilian who accompanies a campaigning army and is in charge of all army supplies, and all administrative, juridical, and financial aspects of the army’s operations and movements (cf. cf. Dictionnaire de l’Ancien Régime, ed. Lucien Bély, 2nd ed. (Paris 2005), 471–2).
 Apparently in corroboration of Baillet, Aubert de la Chesnaye Desbois maintains that René Sain died in Turin in 1623 (Dictionnaire de la noblesse, vol. 14, 428–32). Jean Mesnard however points out that René Sain personally signed the marriage contract of his daughter Françoise in February 1624; the other document cited by Mesnard to show that René Sain was still alive in 1630 concerns Sain’s eldest son, equally called René (Mesnard, ‘Entre Pascal et Descartes: Jacques Habert de Saint-Léonard,’ Travaux de linguistique et de littérature 13 (1975), 111).
 Abraham Tessereau, L’Histoire chronologique de la Grande Chancellerie de France, vol. 1 (Paris 1710), pp. 336, 348.
 The Vidaud (or Vuidaud) family was a family of merchants and bankers in Lyon. The merchant in question is presumably Jean Vidaud the Elder (L’Aisné), who is mentioned in a marriage contract (Lyon, 1614) as an uncle of the groom, also called Jean Vidaud. See the online genealogy of the various branches of the Vidaud family by Gérard Bachelier, URL: http://g.bachelier.free.fr/vidaud.htm (last consulted 29 October 2021).
 André Dechuyes, notary public in Lyon between 1602 and 1639.
 Paris, Arch. nat., Minutier central, ET/LXXXVIII/127 (Nicolas Robinot, public notary). The minutes are digitesed in the context of the project Familles Parisiennes (see www.famillesparisiennes.org). The text quoted is available online, URL: https://nl.geneanet.org/archives/registres/view/43486 (vue 82); last consulted 29 October 2021. Photographs of the manuscript are published in the notice mentioned in footnote [*].
 Louis Videl, Histoire de la vie du Connestable de Lesdiguières (Paris 1638), pp. 412, 422, 435.
 Pierre Borel, Vitae Renati Cartesii compendium (Paris 1656), p. 4.
 Cf. Videl, Vie de Lesdiguières, 410, 421, 464; Pierre de Boissat, Opera seu operum fragmenta (Lyon? 1649?), 40–50 (mention of the presence of François Goyon de Matignon (1607–1675), younger brother of the Count of Thorigny, 43); Baillet’s refers to Nicolas Chorier, De Petri Boessatii … vita (Grenoble 1680), pp. 136, 140, where the author discusses Boissat’s preference for Descartes’ philosophy.
 Didier Kahn, ‘The Rosicrucian Hoax in France (1623–24)’, in William R. Newman and Anthony Grafton (eds.), Secrets of Nature: Astrology and Alchemy in Early Modern Europe (Cambridge MA: MIT Press, 2001), 235–344.