SCIENCE PHOTO LIBRARY SCIENCE PHOTO LIBRARY
Polybius square, artwork. This device, used in encryption and telegraphy, was first described by the ancient Greek scholar Polybius in around 200BC. It works by replacing each letter of the Greek alphabet with a pair of grid co-ordinates. For example, beta (B) would become 12. Polybius conceived of this device as a way of transmitting messages optically with a pair of torches. For an artwork of the system in practice, see image V400/0090.
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