How do you send a private letter, if you don’t have an envelope to seal it in? Before envelopes were invented, people used a variety of techniques to fold paper letters so they could not be opened without breaking the seal.

One set of techniques, used by European monarchs and other big wheels, is called “Letterlocking” [1].   I had never heard of this until recently, but apparently it is a thing, with journal articles [2], web sites [4], a Dictionary of Letter Locking (DoLL) [3],  and YouTube videos and all. 

The basic idea is to fold up a letter into a tamper proof delivery packet. Scholars have described 64 (!) methods, including the elaborate “spiral lock” used by Mary Queen of Scots, Elizabeth I, and Catherine de’ Medici among others [2].

These techniques have been reverse engineered from documents in archives. The point of the process is that…