Scytale Cipher Encryption
The Scytale (pronounced Sy-tally) Cipher was very much used by the Spartans and also by the ancient Greeks and Egyptians. The idea is that you write a message on a ribbon or thin paper or papyrus (hello ancient world) wrapped around an object of a certain diameter, and then to decipher it you need to wrap the ribbon around another object of the exact same circumference so that the letters line up and you can decipher the message. While this wasn’t super secure, in the ancient world it might have been just “good enough” especially during times of war.
This was really fun to do! I tried it out a couple of times with my two nephews and they loved it as well. Simple and ingenious and probably not super effective as far as encryptions go since you don’t really need something the exact same diameter to break the code, just a little imagination (think Wheel of Fortune) and patience. Either way, it illustrates the point and is a nice parlor trick.