How European Royals Once Shared Their Most Important Secrets

A few centuries ago, people used wax seals to secure their letters. This was probably good enough for most people, but seals can be removed and reattached. However, there was a more secure technique called letterlocking that guaranteed that a letter couldn't be opened without it being obvious.

This article from the New York Times describes the technique and its use by royals such as Mary, Queen of Scotts. It's quite fascinating. Watch the video linked in the article which should give you an idea of just how difficult it was to lock a letter using this technique.  

To safeguard the most important royal correspondence against snoops and spies in the 16th century, writers employed a complicated means of security. They’d fold the letter, then cut a dangling strip, using that as an improvised thread to sew stitches that locked the letter and turned the flat writing paper into its own envelope. To get inside, a spy would have to snip the lock open, an act impossible to go undetected.

Catherine de’ Medici used the method in 1570 — a time she governed France while her ill son, King Charles IX, sat on its throne. Queen Elizabeth did so in 1573 as the sovereign ruler of England and Ireland. And Mary Queen of Scots used it in 1587 just hours before her long effort to unite Britain ended in her beheading.

“These people knew more than one way to send a letter and they chose this one,” said Jana Dambrogio, lead author of a study that details Renaissance-era politicians’ use of the technique, and a conservator at the M.I.T. Libraries. “You had to be highly confident to make a spiral lock. If you made a mistake, you’d have to start all over, which could take hours of rewriting and restitching. It’s fascinating. They took great pains to build up their security.”