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Before envelopes existed, privacy was engineered by hand.

[ CYPHER CODE #1156 ]
Letterlocking turned a single sheet of paper into a security system.

[ CYPHER CODE #1157 ]
These folds were tamper evidence.

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If the lock was broken, the message was compromised. 

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Medieval people were thinking like security engineers.

BRIEFING

Jett here. Long before passwords, encryption keys, or two-factor authentication became a thing, Medieval people were thinking very seriously about one thing: who might be reading their mail. So they came up with a security solution that later became an art form. It’s called letterlocking. Let’s get into it.

In the 1500s, envelopes as we know them didn’t really exist, and the postal system was nowhere close to secure. Letters often passed through many hands before reaching their intended destination, and anyone feeling curious or nefarious could try to sneak a look along the way. That meant people sending notes about political secrets, personal confessions, or royal business risked having their private matters spilled all over town.

Something had to be done. So they engineered a solution.

What emerged was something now known as letterlocking, a set of really intricate and quite ingenious folding and sealing techniques that turned a single sheet of paper into its own protective container. This was even better than an envelope because letterlocking was the ultimate security. With nothing more than careful folds, small cuts, weaving paper, and the occasional wax seal, the letter itself became tamper-proof. If someone tried to open it the wrong way, the damage would be obvious. The sneak peek would be evident.

Mary, Queen of Scots, relied on it in the final hours before her execution in 1587. After writing her last letter, she cut a thin strip from the paper, threaded it through the folded packet, and tightened it into what historians now call a spiral lock. Anyone trying to peek would have to break the mechanism, leaving clear proof the message had been intercepted.

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Hundreds of years ago, people developed ingenious methods to secure their letters from prying eyes – and they did it with only paper, adhesive and folds. Late at night on 8 February 1587, an imprisoned Mary Queen of Scots composed her last ever letter to her brother-in-law. "Tonight, after dinner, I have been advised of my sentence: I am to be executed like a criminal at eight in the morning," she wrote. "The Catholic faith and the assertion of my God-given right to the English crown are the two issues on which I am condemned." With a sad acceptance of her fate, she asked him to take care of her affairs and pay her servants, wishing him "good health and a long and happy life". After Mary had finished writing, she then began to fold up the letter to secure its contents. She didn't want her captors snooping – and particularly not her cousin Queen Elizabeth I. However, envelopes were not used in the 1500s – not least because paper was expensive – and there was no trustworthy postal service at the time. Instead, Mary cut a thin strip from the paper margin, before folding up her message into a small rectangle. After poking the knife through the rectangle to make a hole, she then fed the strip through, looping it and tightening it a few times, creating a "spiral lock". No wax or adhesive was required, but crucially, if someone tried to sneak a look, they would have to rip through the strip, so her brother-in-law would know the message had been intercepted.

Once you see how these locks worked, it becomes obvious this wasn’t just careful folding. It was early information security, built by hand.

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As sophisticated as some of these locks were, a few historical figures took letterlocking to an entirely different level.

One of the most formidable was Catherine de’ Medici. The powerful 16th-century queen and political mover-and-shaker was known for using some of the most complex and secure letterlocking techniques of her time. She used carefully engineered paper defenses designed to make interception downright impossible.

What follows shows just how intricate her method could get.

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@verseandsip

Fold a letter like Catherine de Medici: Part I #letterlocking #letterfolding #historicletters #medici @Letterlocking Inspired by Catherine de’ Medici’s concealed spiral-locked letter to Raimond de Beccarie (c.1570). Source: Jana Dambrogio, Daniel Starza Smith, and the Unlocking History Research Group. Title: "Catherine de’ Medici’s concealed spiral-locked letter to Raimond de Beccarie (c.1570)," Letterlocking Instructional Videos. Unlocking History number 0224/Letterlocking Unique Video number: 224. Date filmed: 30 July 2021. Duration: 7:51. Date posted: 10 December 2021. Video URL: https://www.youtube.com/watch?v=U3lGlmRPMKw. Date accessed: 26/02/26.

♬ Badinerie (Main) - Intermede Music

As intricate as the first stage looks, this is where Catherine really starts to flex. The paper isn’t just folded. It’s threaded, pierced, and locked back through itself in a way that makes quiet tampering a pipe dream.

Watch how the mechanism comes together.

SOURCE

@verseandsip

Lock a letter like Catherine de’ Medici: Part II #letterlocking #letterfolding #historicletters #medici @Letterlocking Inspired by Catherine de’ Medici’s concealed spiral-locked letter to Raimond de Beccarie (c.1570). Source: Jana Dambrogio, Daniel Starza Smith, and the Unlocking History Research Group. Title: “Catherine de’ Medici’s concealed spiral-locked letter to Raimond de Beccarie (c.1570),” Letterlocking Instructional Videos. Unlocking History number 0224/Letterlocking Unique Video number: 224. Date filmed: 30 July 2021. Duration: 7:51. Date posted: 10 December 2021. Video URL: https://www.youtube.com/watch?v=U3lGlmRPMKw. Date accessed: 26/02/26.

♬ Badinerie (Main) - Intermede Music

By this point, the real genius of the design starts to show. This wasn’t just about sealing a letter. It was about making sure any attempt to open it would leave obvious damage behind.

SOURCE

@verseandsip

Open Catherine de’ Medici’s letter 🗡️ #medici #letterlocking #letterfolding #historicletters Inspired by Catherine de’ Medici’s concealed spiral-locked letter to Raimond de Beccarie (c.1570). Source: Jana Dambrogio, Daniel Starza Smith, and the Unlocking History Research Group. Title: "Catherine de’ Medici’s concealed spiral-locked letter to Raimond de Beccarie (c.1570)," Letterlocking Instructional Videos. Unlocking History number 0224/Letterlocking Unique Video number: 224. Date filmed: 30 July 2021. Duration: 7:51. Date posted: 10 December 2021. Video URL: https://www.youtube.com/watch?v=U3lGlmRPMKw. Date accessed: 26/02/26. @Letterlocking

♬ Badinerie (Main) - Intermede Music

Now comes the real test. It’s one thing to build a lock this intricate. It’s another thing to try to open it without leaving a trace. Catherine’s design was built to fight back.

Let’s see what it takes to unlock her masterpiece.

SOURCE

@verseandsip

Open Catherine de’ Medici letter: Wax seal method #waxseal #medici #letterlocking #letters

♬ Badinerie (Main) - Intermede Music

DEBRIEFING

Letterlocking is one of those forgotten skills and art forms that reminds us how seriously people have always treated privacy. With nothing but paper, patience, and a lot of precision, they built a system that could signal tampering instantly and protect sensitive messages.

It's so interesting that long before modern cybersecurity became a billion-dollar industry, people were already thinking in the exact same defensive mindset. Different tools, but the same human instinct to protect what mattered most.

NOW YOU KNOW

Sometimes the old solutions were a lot smarter than we give them credit for.