It was an ingenious method for visual message transmission (letter by letter) between mountains of great distance. It was based on a combination of fire signals, invented by Kleoxenes and Demokletus, in the 2nd century B.C. This system may be described as digital (two-digit quinary), a precursor of today’s technology and the only registered attempt of this kind in the world until the 16th century A.D. This relatively simple use of fire signals (for pre-agreed message) in connection with a network of beacons (phryctoriae), first conceived by Pallamedes, was the means through which the fall of Troy was made known to Mycenae in one night by Pallamedes’s assistant, Sinon (Source: Aeschylus, Agamemnon).
Beacons were built on carefully chosen mountains. Each beacon consisted of two walls at the height of a man, with 5 torch holders each, which made it possible to put up 1 to 5 lit torches on each wall at a time. Between the two walls there were special binoculars so that the beacon operator could distinguish the right firelights from the left ones at the beacon of the opposite hill. Moreover, both beacon operators had at their disposal 5 plates with the letters of the alphabet inscribed on them, divided into sets of five. The firelights on the left-hand side of the transmitter’s beacon determined the plate number which had the desired transmitted letter (1 bale-fire put up: the 1st plate was indicated, and so on). The firelights on the right-hand side referred to the desired transmitted letter on that specific plate. (1 torch put up: the first letter was indicated, and so on). The transmission of a message started as follows: the transmitter put up two torches and the receiver confirmed by doing the same, and then both operators brought down the torches. For instance, if two torches were put up on the left wall and four on the right wall, this corresponded to the transmission of the letter “I”.