European royals used to disclose their most vital secrets

According to research, queens such as Catherine de’ Medici, Queen Elizabeth I, and Mary Queen of Scots utilised letter locking technology.

In the 16th century, scribes used a complex security system to protect the most essential royal correspondence from snoops and spies. They’d fold the letter and use a dangling strip as an improvised thread to sew stitches that sealed the letter and turned the flat writing paper into its own envelope. To gain access, a spy would have to snip the lock open, which would be impossible to conceal.