Fryctoria was a means of communication was used in Ancient Greece. The method used two sets of five torches. When a signal needed to be sent, the appropriate torches were lit and placed atop towers called Fryktories, and would be visible to the next tower (usually 20 miles away), and then relayed to the next hill in succession.
It was invented by the Greek engineers Kleoxenis and Dimoklitos in the 2nd century BC. The coding system was as follows:
α β γ δ ε
ζ η θ ι κ
λ μ ν ξ ο
π ρ σ τ υ
φ χ ψ ω
When they wanted to send the letter o (omicron), they opened 5 torches on the right set and 3 torches on the left set.
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