Caesar Encrypted His Military Messages 2,000 Years Before Anyone Called It Encryption

A Javelin Carried a Message Into a Besieged Camp

In the winter of 54 BCE, a javelin flew into a besieged Roman camp in Gaul with a letter tied to it. The camp was commanded by Quintus Tullius Cicero, the younger brother of the famous orator Marcus Tullius Cicero. Enemy forces had surrounded the position so completely that ordinary messengers could not get through. Caesar eventually learned of the siege from a messenger who slipped out of the camp, and he immediately sent a Gallic cavalryman back with his reply. If the rider could not get close enough to deliver the letter safely, Caesar instructed him to fasten the letter to a javelin and throw it into the camp. The plan worked, although the javelin lodged in a tower and went unnoticed for two days before a soldier finally spotted it.

That letter told Cicero that Caesar was already marching to his aid with the legions, giving the trapped Romans a much-needed morale boost. Caesar also mentioned one precaution that makes the story especially interesting today: he had written the message using Greek characters so that an enemy who intercepted it would not immediately be able to read Roman plans.

This particular letter is not necessarily an example of the three-letter shift we now call the Caesar cipher. The famous description of that method comes from Suetonius, writing much later. However, the two accounts together show that Caesar was already thinking seriously about how to protect sensitive military correspondence from being quickly understood by enemy forces.

Key Facts From the Story

• Caesar used Greek letters in a besieged-camp message in 54 BCE.
• Suetonius documented a simple letter-shift cipher in The Twelve Caesars.
• The traditional Caesar shift moves every letter three places forward in the alphabet.
• Augustus used a one-letter shift and had an unusual way of representing X.
• Al-Kindi’s ninth-century work on frequency analysis made simple substitution ciphers far less secure.
• ROT13 is a modern descendant of Caesar’s ideas, often used to hide spoilers or puzzle answers.

The Trick Was Almost Insultingly Simple

Shift Every Letter by Three, and Call It Done

We know the method because the Roman biographer Suetonius recorded it in The Twelve Caesars, roughly 150 years after Caesar’s death. In his account, Caesar handled confidential correspondence with a simple substitution system that replaced each letter with one three places farther along in the alphabet. It is an early, extremely simple example of how a cipher turns readable plaintext into ciphertext.

Suetonius uses D in place of A as his example, which gives us the modern pattern where A becomes D, B becomes E, and Z eventually loops back around to C. Caesar’s Latin alphabet was not identical to the one we use today, so the A-to-Z version is really a modern illustration of the same basic method.

You can see why the system was useful. Once both sides knew the shift, a message could be written and decoded entirely by hand, with no special device or complicated reference table. It would not hold up against anyone determined to analyze the text, but an intercepted letter no longer gave up its meaning at a glance. For military correspondence moving through hostile territory, even that small barrier could be useful.

You Can Still Try Caesar’s C

Source: MakeUseOf News