THE
POLYBIUS
SQUARE
How Ancient Greek Soldiers Sent Secret Messages With Fire — 150 BCE
The Historian's Fire
Polybius was a Greek historian and military strategist who lived through the wars between Rome and the Hellenistic world. Writing his Histories around 150 BCE, he was fascinated by a problem every general faced: how to move a message faster than a man could run.
His answer was to turn the alphabet into numbers. Every letter was given a place in a five-by-five square, named by its row and its column. Soldiers stationed on hilltops and watchtowers then raised torches — the torches on the left counted the row, the torches on the right counted the column. One pair of signals at a time, a whole sentence could cross a valley in minutes.
The Square Itself
Twenty-five cells for twenty-six letters — so I and J share a home, just as the ancients allowed.
Its Long Shadow
Fire Telegraph
The first practical system for sending arbitrary text over long distances.
Nihilist Cipher
19th-century Russian revolutionaries added a key to the square's numbers.
Tap Code
Prisoners of war tapped the same row-and-column pairs on cell walls.