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Cracking the code: Love, war and letters

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This blog was written by Katherine Emery, Assistant Archives Officer.

The English Civil War dates from 1642 to 1651, which ultimately led to the execution of Charles I and England, Wales, Scotland and Ireland being run as a Commonwealth with Oliver Cromwell acting as Lord Protector until his death in 1658. This blog focuses on the Naseby letters from 1645.


Death Warrant of Charles I
Death Warrant of Charles I, 1649, Parliamentary Archives, HL/PO/JO/10/1/297A

The Battle of Naseby (14th June 1645) was a major battle in the English Civil War and a victory for the Parliamentarian side or the ‘Roundheads’. Charles I was forced to flee the battlefield, leaving his men, artillery and personal belongings behind. This included a collection of secret coded letters, which are now known as the ‘Naseby letters’. These letters were found by Cromwell’s forces and taken to Parliament to be deciphered and published later year by order of Parliament, as propaganda against Charles I in the work “King’s Cabinet Opened”.


Naseby letters

The Naseby letters date from between 1641 and 1645, although most of them are from 1645. Roughly half of the letters are written in code, also known as a cipher. Some fully written in code, some only partially in code. The coded letters from Queen Henrietta Maria were also written in French, so the letter would have to be deciphered from code into French and then translated into English, almost like an early form of double encryption.

Letter from Sir Nicholas to Charles I, 22 May 1645
Letter from Sir Nicholas to Charles I, 22 May 1645, Parliamentary Archives, HL/PO/JO/10/1/183/30

This first letter is from Sir Edward Nicholas, a trusted and loyal adviser to King Charles I, who would also serve Charles I son Charles II after the restoration of the monarchy. The letter is dated 22nd May 1645, less than a month before the Battle of Naseby. Unsurprisingly, this letter discusses strategy, including intelligence on the location of Oliver Cromwell and his chief generals of the Parliamentary Army Thomas Fairfax and Richard Browne, as well as the numbers and equipment of Parliamentary Army.

“This day Fairfax, Cromwell and Browne are hither and have with their forces consisting of about twelve 1000 horse and foot and about twenty of Battery and Artillery”

Letter from Lord Jermyn to King Charles I, 12 May 1645
Letter from Lord Jermyn to King Charles I, 12 May 1645, Parliamentary Archives HL/PO/JO/10/1/183/26

This second letter is from Lord Henry Jermyn, a favourite courtier of Queen Henrietta Maria, accompanying the Queen throughout the civil war and later through her exile in France. It is dated 12th May 1645, however unlike Sir Nicholas’ letter this does not discuss politics or strategy but the Queen. Lord Jermyn writes to the King, to keep him updated on the health of his wife, who at the time was ill. He is letting him know that she was slowly getting better.

“shall confime Queens health mends dayly but she is just too weake to give your Majesty an account of it by her own hand some little cough remains that keeping her from sleeping a nights makes her strength returne but slowly”

Letter from Queen Henrietta Maria to King Charles I, 6 January 1645
Letter from Queen Henrietta Maria to King Charles I, 6 January 1645, Parliamentary Archives, HL/PO/JO/10/1/183/11

This third letter is from Queen Henrietta Maria, dated 6th January 1645, prior to Lord Jermyn’s letter describing her illness. This letter has a very different tone to the King’s other letters, discussing both safety and politics. Henrietta cares for and is worried for Charles moving around in such a dangerous time without any form of guard.  Later in the letter she discusses politics, advising Charles to be loyal to their royalist followers and potential foreign Catholic alliances.

“I doe not see how you can bee in safety without a Regiment of Guards”

“doe not abandon those who have served you for fears they doe forsake [leave] you in your need”

 “if afterward there should bee noe peace you could never expect succours [aid] either from Ireland or any other Catholick Prince for they would believe you would abandon them after you have served your self.”

Draft letter from King Charles I to Queen Henrietta Maria, 7 May 1645
Draft letter from King Charles I to Queen Henrietta Maria, 7 May 1645, Parliamentary Archives, HL/PO/JO/10/1/183/25

This final letter is a draft letter written by King Charles I, dated 7th May 1645. We only have draft letters from the King, as this collection of letters was found from his bags, so would only contain letters sent to him and drafts of letters he planned to send to others. This letter continues to discuss strategy and army movements with his wife. Excitedly sharing good news from the Royalist army which were departing from Oxford on this day.

“my Affaires are in a very hopefull way and to bring a good omen to the beginning of my march werry good newes was brought me from Wales this morning"

But the letter still begins “Deare heart” and ends “farewell deare heart”, which is how many of the letters between Charles and Henrietta begin and end (or Mon cher in French meaning ‘sweetheart’). This shows that even through the trying times, separated during a civil war, they still had a loving relationship.


Babington Plot

The Babington Plot, similar to the Naseby letters, were a series of secret and sometimes coded letters. The Babington Plot dates to 1586, approximately 60 years earlier than the Naseby letters. The chief conspirator Anthony Babington planned to assassinate the Protestant Queen Elizabeth I and put the Catholic Mary Queen of Scots on the throne.

Mary was imprisoned in Chartley Hall, Staffordshire and where she received these secret, coded letters from her followers and foreign catholic allies. These letters were couriered by Gilbert Gifford, who transported them through specially made hollow corks in beer barrels.

The key letter was from Babington on 6th July 1586, detailing to Mary the assassination plan. On 17th July 1586, she sent back her reply approving the plan and sealing her fate. All of these secret letters had been intercepted, as Gifford was a double agent working for Sir Francis Walsingham. Walsingham was the Principal Secretary to Queen Elizabeth I and was known as the ‘Spymaster’. These coded letters were written in a simpler code than the Naseby letters and were decoded by Thomas Phelippes, a master linguist and code analyst.

Mary and Babington trusted and relied on the code to hide their messages, and so openly discussed their assassination plot. This was their downfall, the Babington Plot coded letters became the main piece of evidence in Mary’s trial. And later led to her execution at Fotheringhay Castle, Northamptonshire the following year in 1587.


Record of the Trial of Mary, Queen of Scots
Record of the Trial of Mary, Queen of Scots, Parliamentary Archives, HL/PO/JO/10/14/2A

Medieval Codes

Coded letters were relatively common in political letters, especially those involving espionage and conspiracy. The main type of code (or cipher) used in this period was the substitution cipher. A substitution cipher would substitute a letter with a different letter, symbol or number, e.g. a=1, b=2, c=3 and so on. Over time variations of this cipher developed as people like Thomas Phelippes learnt how to crack them.

The code that Mary and Babington used was a variation of the substitution cipher, called a nomenclator cipher. This meant that not only every letter had a symbol or number assigned to it, but words, phrases, names, prefixes and suffixes. This required a full page key with all the different symbols and values, in order to decipher it. But due to the frequency of common letters and phrases like ‘a’, ‘e’ and ‘the’, it could still be decoded by Phelippes.

The Naseby letters learnt from Mary’s mistakes and instead used a homophonic substitution cipher. This assigned multiple symbols or numbers to the more frequent letters like ‘a’ and ‘e’, so it would be harder to decipher. For example, in this letter from Henrietta Maria to Charles I the letter ‘e’ (in red) has at least 5 different numbers (22, 33, 51, 58, 65) assigned to it, whilst the letter ‘y’ (in blue) only has 1 number (40).


Letter from Queen Henrietta Maria to King Charles I, 13 March 1644
Letter from Queen Henrietta Maria to King Charles I, 13 March 1644, Parliamentary Archives, HL/PO/JO/10/1/183/17

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