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Mary Queen of Scots’ lost letters are finally cracked by codebreakers.

Cipher between Mary and Châteauneuf

Newly found letters, written by Mary Queen of Scots while in prison, decoded by trio of codebreakers

Example of a Mary Queen of Scots enciphered letter

A group of international codebreakers has uncovered a set of secret, coded letters written by Mary Queen of Scots while she was imprisoned in England by Queen Elizabeth I. The contents of the letters were believed to be lost until computer scientist George Lasry, pianist and music professor Norbert Biermann, and physicist and patents expert Satoshi Tomokiyo discovered them while searching the online archives of the Bibliothèque nationale de France.

The codebreakers solved Mary’s sophisticated cipher system and found more than 50 new scripts previously unknown to historians, which date from 1578 to 1584. The letters, addressed to Michel de Castelnau de Mauvissière, the French ambassador to England, provide new insight into Mary’s captivity and include complaints about her poor health and captivity conditions, negotiations with Queen Elizabeth I for her release, and her mistrust of Elizabeth’s spymaster Sir Francis Walsingham.

Mary Queen of Scots sends secret messages from her prison cell

Mary Queen of Scots was one of the most famous historical figures of the 16th century. She was next in line for the English throne after her cousin Elizabeth, but since she was seen as a threat, Elizabeth had her imprisoned for 19 years. Eventually, Mary was executed for her alleged involvement in a plot to kill Elizabeth.

Mary cipher resembles Castelnau’s cipher from his time as ambassador in London

While in captivity, Mary kept in touch with her associates and allies through secret communication. We know that there was a confidential channel between Mary and Michel de Castelnau de Mauvissière, the French ambassador to England. But now, codebreakers have found evidence that this exchange started as early as May 1578 and lasted until mid-1584.

The codebreakers used computerized and manual techniques to decode the letters, which show the challenges Mary faced in staying connected to the outside world, and how the letters were carried and by whom. The letters talk about Mary’s complaints about her health and captivity, her negotiations with Queen Elizabeth for her release, and her mistrust of Elizabeth’s spymaster Sir Francis Walsingham, among other things.

The codebreakers stumbled upon the letters while searching for enciphered documents in the archives of the French National Library. At first, the letters were thought to be from the first half of the 16th century and related to Italian matters, but after cracking the code, the codebreakers realized they were written in French and had nothing to do with Italy. They confirmed the letters were from Mary after comparing them with plaintext letters in the British Library. In total, they found 57 letters with the same cipher.

Mary Queen of Scot’s letters decoded

Here are a few samples of Mary Queen of Scot’s decoded letters.

January 20, 1580 Mary to Castelnau, Sheffield

Monsieur de Mauvissière, since with the forthcoming arrival of the Duke of Anjou, my brother-in-law, in this kingdom various rumors are being spread as much to his disadvantage as to irritate his best friends against him and to put them in distrust of his good and upright intention toward them, I will only tell you that you must advise the said Duke, when he is here, not to persist in the request that he is said to have made for the rehabilitation of the Earl of Leicester, whom he does not need in order to fortify himself, and he needs even less to fear [Leicester’s] strength and power if he takes care of it in good time. I know that some Catholics have already been greatly offended by this,Footnote132 fearing to see themselves again under the persecutions of the past. Such fear will make them constantly affectionate toward the Duke of Anjou, all the more so if they see him animated against their common enemies.

Apologize to him on my behalf for not having written to him yet, for fear of putting him under suspicion and of harming his negotiations, which however I will not fail to assist with everything I can through my friends. As I have already written to you, I leave to his courtesy and your kind intercession the good services I hope for from him for [the improvement of] my treatment in this captivity, the preservation of my person and of my rights in this kingdom.

I would like very much to pursue a second visit to my son, considering the present state of affairs in Scotland, which seems quite appropriate, but I fear the suspicions that may arise in various places, so I am of the opinion that I should wait until after the wedding, which I am being assured will be before this Lent.

If in this next parliament the succession is dealt with, please remember to speak to the queen of England on my behalf and to make the same pleas that I previously wrote to you on the same subject and occasion, by repetition of which I am not going to prolong this letter, but for praying to God to keep you in his holy protection.

Written in Sheffield this twentieth of January.

16 Apr 1583, Mary to Castelnau, Sheffield

Monsieur de Mauvissière, I would have very much liked this bearer to have been able to delay his departure for a few more days so that through him I could give you some certainty on the negotiations with Beale, into which he has so far entered only superficially, having made to me some overtures for my deliverance, restoring the affairs in Scotland and a good friendship between his mistress, myself and my son and our states, but in too general terms for one to rely upon, myself being similarly restrained from entering into any particulars, seeing that the said Beale is not credited nor authorized for this purpose by any letter, memorandum or instruction by the queen of England nor of those of her council so that, as I told him, any treaty between him and me [achieved] in this way would neither be solid nor substantial, but would only serve to unnecessarily uncover my intentions, which seemed to be his principal charge; I was not inclined to give him assurances this would come to any effect, remembering too well the little that had resulted from my conferences with him on his last visit, to believe he was sincerely proceeding as a man of goodwill.

This is where things stand; I will not fail to keep you informed of what will follow hereafter, and nevertheless I thank you for your good and ample advice in your last (letters) which the said Beale brought me, according to which, if things make some progress hereafter, I may well request that I be allowed to send Nau to the queen of England to propose and explain to her on my behalf what I would like to commit only to her, and I would not find it inappropriate for you to make an appeal for it right now, but if it is necessary to enter into a treaty and if there is hope of coming to a conclusion, it will be convenient for me to employ several people of greater quality whom I can send to join him for further instructions on all the necessary matters of which he has long been well informed. I cannot thank you enough for the care, vigilance and entirely good affection with which I see that you embrace everything that concerns me and I beg you to continue to do so more strongly than ever, especially for my said release to which I see the queen of England quite inclined. If it brings any success, be assured that I will acknowledge as much as I can your good services with her, and the obligation I have for you from the past. Sheffield, this sixteenth of April.

May 1583, Mary to Castelnau, Sheffield

Monsieur de Mauvissière, you have given me great pleasure in informing me amply, as you have done in your last two letters, of your proceedings on this new offer and negotiations for my freedom, on which I cannot give you any solid details until I see the outcome of Beale’s report on his dealings with me on this subject, [Beale] having promised me upon his departure to inform me about it as soon as he can and to sincerely do everything in his power to help. Now, if beforehand he refrains from writing to me as openly as would be necessary on this matter – on which I would not wish to press him, I beg you to confer with him and to indirectly find out, if you can, the intentions of this queen and those of her council on this matter, for I think that the said Beale will commit it to you more readily than to his quill.

I will still wait before requesting [permission for] Nau’s journey until the things which I wrote to you about recently are further advanced, since he has begged me to do so.

The journey of my host, as I understand it, has been delayed or rather canceled, but I could not imagine any reason for this, other than their wanting to include him in the commission they will send to deal with me, for so far I do not see that their intention is to have me there as it seems that this spy, of whom you wrote to me in your second letter, has reported to you. But in truth, I do not quite understand what he means by these words, that their intention is to pull me there and not to conclude anything here. I beg you to clarify this for me in the first letters you write to me.

I do not find in Monsieur de Mainneville intentions anything but appropriate, but beware that by intimidating this queen in vain and not succeeding in obtaining my release, you might cause her to issue more precise and strict orders for my custody and treatment here. I thank you for the good advice you gave me to request the Queen Mother, if she proceeds with her travel to Calais, to diligently send some gentleman to assist me on her behalf in this request for my freedom. Please kindly apologize on my behalf to the Queen Mother that I don’t write to her directly, as I do not dare to commit anything not in cipher via this channel, and via the ordinary one, my letter would not fail to be discovered.

I have written to the queen of England as you have advised me, and by word of mouth I have instructed Beale, as he sees fit, to convey to Burghley, Leicester and Walsingham and others of the Council the sincerity of my intention toward their said queen, themselves, and this state, with assurances on my part against any innovation in the future if this treaty takes effect. You can also confirm this to them; and as far as the king, my brother-in-law, is concerned, the best thing you could do for me in his name would be to promise that he will take part in the agreement and treaty which will take place on this matter between the queen of England, myself and my son, validating it by his own signature, remaining as the guarantor on either side for the performance of the treaty.

If the Sieur de Mainneville passes through this country, as it is said he would do, I would ask you to thank him on my behalf for his good services in Scotland, for which I feel very much obliged to him, and to make sure to obtain from him a report as detailed as possible on his negotiations with my son and with those of the good party in Scotland, and on the state in which he has left matters there. If he wishes to write to me directly, you will deliver to him the enclosed cipher alphabet so that he can then use it if he is further involved in my affairs.

Do not forget what I have previously sent you about entering into business with Colonel Stewart, and to this end I think that an offer of a good pension would be of great use, if it would please the King of France to grant him one. Bring back to him the good memory and opinion of him, as you have heard, that always remain with me for the good service he did between the late Madame de Lennox and me and that, if he is willing to assure me of his loyalty and entire devotion toward myself and my son, in accordance with his duties, I will give him more honors and grades than he will ever receive from this queen who uses him only for the moment.

Convey to Archibald Douglas the resentment which I still have for the unworthy and bad treatment which he has received [because of his actions] on my behalf, which I will receive as a full proof of his loyalty and sincere intentions toward me, so that I shall reward him if God ever gives me the means for it. About the conditions which have been offered to him by Walsingham I think that he would be better off agreeing to retire in Scotland where he will not fail to maintain such intelligence as he may want with the said Walsingham, to obtain what he can out of it, and he will not be in danger nor remain so obliged toward this queen as she would pretend to support him there, but he should take good precautions beforehand to provide for his safety in Scotland, where it would give me great pleasure if he could win the Earl of Angus back, and [re]assure my nephew of Bothwell.

Give Fowler ten pounds Sterling on my behalf and assure him that if he continues to faithfully impart to you the intelligence he will obtain from Scotland, and to serve me wherever you will employ him, you will give him an honest reward which indeed I would not refuse him once I were well assured of his fidelity, and I could even grant him some annual pension.

I have written to Monsieur de Glasgow to take hold of this girl of the Laird of Grange and appoint her to one of my relatives in France; however, I thank Madame de Mauvissière for demonstrating her goodwill in this matter, for which I will forever be obliged to do the same for all your relatives whenever I will have the occasion; whereupon, commending myself to your good graces, I pray to God that he may keep you, Monsieur de Mauvissière, under his holy and worthy protection. Sheffield, the fifth of May according to the old computation.

The following is from Nau to Monsieur de Mauvissière.

Monsieur, I kiss your hands for the favorable remembrance you have of me, who will always remain your faithful servant. I am sending to this honest man Foster the patent for his pension, having nothing further to write than if it pleases you to retain him longer, I beg you to accept him as your servant, in order to exempt him from malevolence and from being chased by others who would trouble him without your protection.

30 Oct 1584, Mary to Castelnau, Wingfield

The main topics I am writing to you about:

1° My transfer from here,Footnote291 which I was told was firmly decided, either to Sir Ralph Sadler, a good man, or to the Earl of Rutland,Footnote292 or to Lord Saint Jon.Footnote293


However, please continue to pursue as soon as possible [an authorization for] Nau’s travel over there,Footnote294 and in particular, raise the topic on my behalf with the Earl of Leicester, reminding him of the promise he made to make this happen, and even have Nau tell him verbally what I cannot put in writing. I recommend assisting the said Gray for his negotiations there, in case he needs your assistance or the assistance of the king.


Do not forget to inform the said Courcelles of your ideas and good advice about my estate and affairs there. Beware of Archibald Douglas, for he has not been as sincere as he would like you to believe, and in particular, make sure he doesn’t learn anything from you about Gray’s negotiations.


This is all I can report on now, being under pressure to dispatch this letter, so that it can reach Gray there in time, and I will conclude with my affectionate recommendations etc.

Date and place unknown, Mary to Castelnau

You should express your friendship in every possible way toward this messenger, and speak highly of his mistress, the Countess of Shrewsbury, mentioning my confidence in her friendship and goodwill, and that in return, she should continue with the good services she did for me in the past, of which you have learned when she was at the court. Also mention that you know of several noblemen in this country who are devoted to the countess but are deeply sorry that there is a divide between me and her, and in conclusion, for her own good, the Countess should appreciate and preserve the duty assigned to her,Footnote296 more than anyone else in this country. Being sure that you will not omit anything useful, I do not need to remind you to let him know of the goodwill toward me of the king, my brother-in-law, who also puts forward my rights in this country.Footnote297 Make sure not to reveal anything of importance to this messenger, regarding my affairs or those of the king, as any such would be passed on. Please find some way to communicate with Lord Burghley, and let me know of his opinion on what I wrote to you in a letter you should receive by Thursday.

Other interesting Mary Queen of Scots letters

Here are more interesting Mary Queen of Scots letters that are housed in UK’s National Archives.

February 25, 1588 Sir Edward Stafford to Elizabeth

Sir Edward Stafford to Elizabeth SP 78 18

I spake yesternight with the King, who sent for me by a man quite unknown, to a house that I think I can guess at again, though it were in the night, and that he brought me far out of the right way to it; where I found nobody in the chamber but himself. In the house I heard folks, but nobody saw me nor I saw nobody, for that he brought me tarried not in the chamber. The King began with me… that whatsoever he delivered me, I would send it directly to your Majesty’s own hands, and that you would do what lay in you for the good of France, and keep it to yourself…

uppon my promis that I and your Majesty woolde performe ytt in all points, that he woolde deale plainly with me, and laye his state more open to QM then ever he did to any; that he was verie well contented Q should take advice of anie the secretest cownselors whome yt pleased her, that he knew she had them that she did assure should doe nothing passing her commandement, that he wisshed with all his hart to have given of his bloude that he had the like woolde depend uppon noe bodie but uppon his will, his affayres should not (as he termed ytt) pendre a la balance as theie doe…I hoped of anie thing else from him but that he woolde deale more pleinly with her Majestie, beseching her with all his hart to doe ytt, and without making knowen to anie that anie request came from him because they of ye religion as he saied coulde kepe nothinge secret, and that she woolde perswade the King of Navarre to have a care of his estate, and to accomodate him self with the French King in suche sort as the king mought have noe more pretence to ruine France and them bothe; wheruppon I replyed to him the impossibilitie that ytt was for the Queen’s Majestie to deale with the King of Navarre in religion…that ytt was a thing she woolde not meddel in…’

December 22, 1593 Elizabeth I to James VI of Scotland

This letter has been modernized by ChatGPT.

Hey there, brother. I’m sad to see that a king is being misled, his council is being abused, and his kingdom is going down the wrong path. I love you and don’t want to see you ruined, so I’m keeping a close eye on your safety. If I didn’t care, I could ignore what’s happening, but I won’t let my enemies win. If you’re being swayed by people who are lying to you, I’ll tell you the truth and help you avoid harm.

I was shocked when I read your last message to me. Who with a clear head could think that any answers you’ve written to me would satisfy someone who isn’t naive and who left out the fifth thing? You had clear evidence of the rebels in the field, and you knew about the big offers they made to foreign princes. But now, even though everyone knows about it, you’re pretending it never happened, and you can’t find a jury for them. This is crazy! If a weak and slack government appears, bold spirits will steer the ship to the biggest wreck, and they’ll take advantage of the failure. Don’t be so hard on yourself.

The greatest danger to a king is accepting bad accounts because they’ll make fun of you and take advantage of your neglect. If a prince shows fear or yielding, he’ll have enough tutors, even if he’s still a minor. When I think about the punishment these wicked traitors deserve, I read your message again, but when I reread it, I was shocked to see how childish and foolish the best of the three excuses you got from them were. They turned their treason bills into accounts for artisans with items for expenses, but they didn’t mention the one item they deserved the most: the cord for their well-deserved office. How can you accept this bitter medicine that’s meant to get rid of them instead of being worthy for a king’s acceptance?

I’ve never heard such a mocking insult. If I were you, they would learn a quick lesson. The best thing I can say about your letters is that I can see that your judgement is good enough to not affirm the truth of what they’re saying, but you’re letting them say it. How can you not have a law for people who, if their denial was ever accepted, would save their lives when their treason is so obvious, even the messenger wouldn’t have made it up if it wasn’t true.

No one should ever be found false if their denial could save their life. In a prince’s case, many circumstances can provide a good defense for a king who wants to show it. And they won’t lack ministers who won’t deny it themselves. So please, don’t use these excuses. They’re too thin to save you from getting wet. For your own sake, act like a king and show your subjects that you respect yourself, and don’t hide or suffer danger and dishonor.

To let you know my opinion, judgement, and advice, I’ve chosen this noble man who I know is wise, religious, and honest. I want you to trust him as if I were there, and please bear with my straightforwardness. If my love didn’t exceed all limits, I wouldn’t have gone so far.

I pray that God blesses you and keeps you from the advice of people who care more about themselves than you. I wish you many years of reign.

elizabeth i to james vi december 1593

The Tide Letter, Noon, March 17, 1554

This was one of the most important letters that Elizabeth ever wrote. She had been imprisoned by her half-sister Mary on suspicion of involvement in the Wyatt rebellion, which aimed to overthrow the queen because of her determination to marry Philip of Spain. Having heard that she was to be taken to the Tower, Elizabeth wrote in a desperate attempt to secure an audience with her sister. Fearing that her enemies might alter the text, she struck lines across the blank space above her signature.

Your Majesty, I humbly ask that you verify the old saying that a king’s word is worth more than another man’s oath in my case. Remember your last promise and my last request that I not be condemned without a fair trial and evidence, which it seems I am being now without cause. I pray to God that I die the most shameful death if I have ever meant any such thing. I swear before God (Who will judge my truth, no matter what malice may be plotted) that I have not practiced, conspired, or consented to anything that could harm you or be dangerous to the state in any way.

Therefore, I humbly ask Your Majesty to allow me to face you in court and not to rely solely on your counselors. If possible, let me answer before I am sent to the tower, or before I am further condemned. I assure you that I am innocent and that my hope in your natural kindness will not allow me to be cast aside without reason. I only wish that you truly knew the truth, which I believe you will never know from just reports.

Once again, I humbly kneel (since I am not allowed to physically bow) and ask to speak with Your Majesty. I would not be so bold if I did not know myself to be innocent. As for the traitor Wyatt, he may have written me a letter, but I swear on my faith that I never received any from him. And as for the copy of my letter sent to the French king, I pray to God to condemn me eternally if I ever sent any word, message, token, or letter to him by any means. I will stand by this truth until my death.

I only ask for one word of answer from you.

I am and always will be Your Majesty’s most faithful subject.


page of cyphers sp 53 22

Image Credits

In-Article Image Credits

Cipher between Mary and Châteauneuf via Taylor Francis Online with usage type - Public Domain
Mary cipher resembles Castelnau’s cipher from his time as ambassador in London via Taylor Francis Online with usage type - Public Domain
Example of a Mary Queen of Scots enciphered letter via Taylor Francis Online with usage type - Public Domain

Featured Image Credit

Cipher between Mary and Châteauneuf via Taylor Francis Online with usage type - Public Domain


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