Phryctoria

Phryctoria (φρυκτωρία) was a semaphore system used in Ancient Greece. The phryctoriae were towers built on selected mountaintops so that one tower (phryctoria) would be visible to the next tower (usually 20 miles away). The towers were used for the transmission of a specific prearranged message. One tower would light its flame, the next tower would see the fire, and light its own.

In Aeschylus tragedy Agamemnon, a slave watchman character learns the news of Troy's fall from Mycenae by carefully watching a fire beacon. Thucydides wrote that during the Peloponnesian War, the Peloponnesians who were in Corcyra were informed by night-time beacon signals of the approach of sixty Athenian vessels from Lefkada. When Cnemus attacked Salamis Island, the Salaminians informed they Athenians and asked for help by beacon-fires.

Phryctoriae and Pyrseia
Ιn the 2nd century BC, the Greek engineers from Alexandria, Cleoxenes (Κλεόξενος) and Democletus (Δημόκλειτος) invented the pyrseia (πυρσεία). Πυρσεία from πυρσός which means torch. The letters of the Greek alphabet were listed on a table. Each letter corresponded to a row and a column on the table. By using two groups of torches (five torches in every group), the left indicating the row and the right the column of the table, they could send a message by defining a specific letter through combination of light torches.

The coding system was as follows:

When they wanted to send the letter O (omicron), they fired five torches on the right set and three torches on the left set.