Mary, Queen of Scots used a complicated “letterlocking” process to conceal the secrets of the last letter she wrote before she was beheaded, researchers have discovered.
Written in French on 8 February 1587 to Henry III, king of France from her prison cell, the letter sees Mary write that she has “been advised of my sentence: I am to be executed like a criminal at eight in the morning.
“I have asked for my papers, which they have taken away, in order that I might make my will, but I have been unable to recover anything of use to me, or even get leave either to make my will freely or to have my body conveyed after my death, as I would wish, to your kingdom where I had the honour to be queen, your sister and old ally,” writes Mary, in a translation provided by the National Library of Scotland, where the letter is held.
Now an international team of researchers have found that Mary used a delicate folding process to seal the letter, ensuring that any tampering would be immediately obvious to its recipient. The researchers, from universities including King’s College London, MIT and Glasgow, are part of the Unlocking History group, and have been exploring the historical process of “letterlocking”, in which letters were folded to become their own envelopes, before envelopes were invented.
Earlier this year, they managed to read an unopened letter written in 1697 without breaking its seal, using X-rays to see inside the document slice by slice, and create a 3D image. Now, as part of research that has seen them look at 250,000 letters, they have discovered the technique of the “spiral lock”, which was used by Elizabeth I as well as her executed cousin Mary, along with politicians, ambassadors and a correspondent of Sir Francis Walsingham, Elizabeth’s spymaster.
“One of the most spectacular examples of spiral locking … is Mary’s last letter,” they write in an article which was published on Friday in the Electronic British Library Journal. “The letter’s contents are powerful and moving: written on the eve of her execution, it acts not only as a letter – a document intended to be sent to and read by someone at distance – but also a last will and testament and a bid for martyrdom. It is sometimes said that writing the letter was Mary’s last act; in fact, after she wrote it, the letter had to be folded and secured shut. After writing her last message, Mary used letterlocking to prepare it for delivery.”

The academics, who include Jana Dambrogio of MIT Libraries and Daniel Starza Smith from KCL, write of how challenging it is to explore the process of letterlocking, because the letter packets are “designed to be broken” by their recipients. The spiral lock requires more than 30 steps to complete, a mix of folding and slits and sometimes adhesive, to prevent unwanted readings. It is, they say, “a highly intricate technique that required time, patience and great skill: one wrong move and your locking mechanism could break and you would have to start the letter again.
“The mechanics of this lock force the person opening the letter to tear the lock apart in order to access the contents,” write the academics. “Because the lock breaks in multiple places, it is impossible to piece back together in a way that would allow it to pass through the slits again; if someone thought their correspondence had been tampered with, it would be relatively simple to detect.”
The article identifies the folds and slits that show that Mary’s last letter was locked, adding that “because it is written in Mary’s own hand from her prison cell, we have reasonable grounds to believe she locked it herself”.
Dambrogio said: “Mary’s last letter is a document of enormous national importance in Scotland and its contents are well known. But working with it in person and figuring out its unique spiral lock was thrilling as a researcher – and a real a-ha! moment in the study of letterlocking,”
“The letter is a powerful and moving document written on the eve of Mary’s execution, not only a letter but also a last will and testament of sorts. But our big discovery is that after she wrote the letter she used one of the most elaborate and secure letterlocking methods to seal it. Not only that, she uses a variation of the technique – a single large slit rather than a run of small ones – which may testify to the limited tools she had available in her final hours.”
A letter by Catherine de’ Medici from 1570 and one written by Elizabeth I in 1573 to Henry III, in which she expresses her surprise at Henry’s suggestion of her possible marriage to the king’s younger brother François, are also identified by the article as having been sealed with a spiral lock. The research is part of the British Library’s exhibition Elizabeth and Mary: Royal Cousins, Rival Queens.
“Letterlocking is one of the most important communication techniques the world has known, but its history is only just coming to light,” said Smith. “For some 600 years, virtually all letters were sent using letterlocking, before the invention of the modern gummed envelope in the 19th century – it was as important to epistolary communication as computer coding is to emails today. The study of letterlocking supplies us with rich information about the concern historical figures had with communication security, and it also testifies to the inventiveness and even aesthetic creativity with which they responded to these concerns. The fantastically intricate spiral lock brings all these aspects together.”