More than two millennia before encryption became a routine feature of messaging apps, Julius Caesar understood that military communications often travel through hostile territory. During the Gallic Wars, he scrambled messages with letter-shifting techniques that later writers called a cipher, giving historians one of the earliest documented examples of cryptography in action. His methods were simple enough to use by hand, yet effective enough to keep an enemy from reading a battle plan at a glance.

Key facts at a glance

• Caesar left one of the earliest recorded examples of military encryption in his Gallic War campaigns.
• He used Greek characters to disguise a message to his legate Quintus Tullius Cicero in 54 BCE.
• The Roman historian Suetonius later described a Caesar cipher in which each letter shifts three places forward.
• A modern English example is ATTACK AT DAWN becoming DWWDFN DW GDZQ.
• Augustus used a similar system, but with a one-letter shift and a peculiar way of writing X.
• Frequency analysis, described by Al-Kindi in the ninth century, made simple substitution ciphers far less secure.

A message thrown into a besieged camp

In the winter of 54 BCE, a javelin flew over the ramparts of a Roman camp in Gaul with a letter tied to its shaft. The camp belonged to Quintus Tullius Cicero, younger brother of the orator and a legate under Caesar’s command. Enemy forces had surrounded the position so completely that ordinary communication was impossible. Caesar learned about the siege only after a messenger managed to slip through the lines and reach him. He immediately prepared a relief force, but he still needed to tell Cicero that help was coming.

Caesar ordered a Gallic cavalryman to carry his reply. If the rider could not approach the camp safely, Caesar told him to tie the letter to a javelin and hurl it over the fortifications. The rider did exactly that. The javelin struck a tower and stayed there for two days before a soldier noticed it, but the message finally reached Cicero. It promised that Caesar was already on the move with his legions, a vital piece of news for Romans who had been wondering whether relief would arrive.

The letter also revealed Caesar’s instinct for security. He had not written in ordinary Latin.

Source: MakeUseOf News