Eric encrypts a secret message employing the Caesar box cipher code which was used by the army of the Roman emperor, Julius Caesar, more than 2,000 years ago! It's not magic ... it's mathematical! The pedagogical side: To decrypt a secret message, you need a key, or shared information about the structure of the cipher. In the example, a message that is 16 letters long is written in boxes across a square grid and then read by column.