Caesar's Secret Shift

Julius Caesar had a massive problem. In the first century BCE, his military campaigns stretched across the world. He constantly sent runners through enemy territory carrying highly sensitive orders. If a messenger was captured, Caesar’s battle plans were ruined. He needed a way to make his letters look like complete gibberish.

His solution was brilliantly simple: he just slid the alphabet forward. Caesar chose a shift of exactly three steps. If he wanted to write an A, he counted three letters down and wrote a D. A B became an E, and a C became an F.

When he reached the end of the alphabet, he just wrapped it around like a circle. An X, Y, or Z looped back to become an A, B, or C. To read the message, his generals simply shifted every letter three spaces backward.

You might think shifting three letters is a terrible way to hide a secret. Today, it is! But back then, most of Caesar's enemies couldn't read at all. Even the few who could had never seen a substitution cipher. That simple shift was all he needed.