It's tempting to think that spy gadgets aren't all that old, but even Caesar encoded messages using cryptography. This disk dates back to the Civil War, when it was used by the Confederate side -- CSA stands for Confederate States of America. It's pretty obvious how the device works: rotate the inner wheel to displace the letters. M = G, P = J, etc. Simple to crack, right? Not if the message is written in a language you don't know. Spies were tricky like that.