Asked to name the last act of Mary, Queen of Scots, before her execution in 1587, amateur historians might say she wrote a letter to her brother-in-law, Henry III of France. But one important act came after the writing of the letter—Mary had to lock it up, in a sense. And researchers say she did so in "one of the most spectacular examples of spiral locking" they have seen in a new study published in the Electronic British Library Journal. The concept of "letterlocking" was familiar in that age, one before the advent of gummed envelopes, notes CNN. Essentially, Mary had to turn the paper on which she wrote her letter into its own envelope to ensure privacy.
As the Guardian notes, this is much, much easier said than done, involving a series of intricate folds and slits. The spiral lock used by the queen, for example, would have required more than 30 such moves, and if even one went wrong, it could ruin the whole process. Ars Technica describes it as a "paper lock that featured an intricate spiral mechanism," and Mary's lock is "particularly ingenious and delicate because it incorporates a built-in self-destruct feature." That is, if someone had tried to read or tamper with the letter before it got to Henry III, he would have known, because the lock could not have been reassembled. (You can get a sense of the process in this video.)
"I am to be executed like a criminal at eight in the morning," the 44-year-old Mary writes from her prison cell on the eve of her execution. Because the letter was written in her own hand, researchers presume she locked it herself, too. "Mary’s last letter is a document of enormous national importance in Scotland and its contents are well known," says Jana Dambrogio of MIT Libraries. "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." (A dental scanner has helped researchers read locked letters without destroying them.)
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