In the 9th century, during the Arab–Byzantine wars, the Byzantine Empire used a semaphore system of beacons to transmit messages from the border with the Abbasid Caliphate across Asia Minor to the Byzantine capital, Constantinople.
According to Byzantine sources (Constantine Porphyrogenitus, Theophanes Continuatus and Symeon Magister), the line of beacons began with the fortress of Loulon, on the northern exit of the Cilician Gates, and continued with Mt. Argaios (identified mostly with Keçikalesı on Hasan Dağı, but also with Erciyes Dağı near Caesarea), Mt. Samos or Isamos (unidentified, probably north of Lake Tatta), the fortress of Aigilon (unidentified, probably south of Dorylaion), Mt. Mamas (unidentified, Constantine Porphyrogenitus has Mysian Olympus instead), Mt. Kyrizos (somewhere between Lake Ascania and the Gulf of Kios, possibly Katerlı Dağı according to W. M. Ramsay), Mt. Mokilos above Pylae on the southern shore of the Gulf of Nicomedia (identified by Ramsay with Samanlı Dağı), Mt. Saint Auxentius (modern Kayış Dağı) south-east of Chalcedon (modern Kadıköy) and the lighthouse (Pharos) of the Great Palace in Constantinople. This main line was complemented by secondary branches that transmitted the messages to other locations, as well as along the frontier itself.
