Leo I, also Levon I or Leon I, (unknown – Constantinople, February 14, 1140 is the fifth lord of Armenian Cilicia or “Lord of the Mountains” (1129/1130-1137).
He learns to exploit the open, yet restrained, hostilities between the Byzantine Empire and the Frankish principalities of Edessa and Antioch.
Most of his successes benefit from Byzantium’s preoccupation with the threats of Zengi (the atabeg of Mosul) from Aleppo and the lack of effective Frankish rule, especially in the Principality of Antioch.
He expands his rule over the Cilician plains and even to the Mediterranean shores.
In his time, relations between the Armenians and the Franks (the Crusaders), two former allies, are not always as courteous as before: a major cause of dissension between them is the ownership of the strongholds of the southern Amanus (today Nur Mountains in Turkey), and on the neighboring coasts of the Gulf of Alexendretta (the Gulf of İskenderun in Turkey).
Leo is defeated decisively by the Byzantine Emperor John II Komnenos, who successfully lays siege to his fortresses.
Leo and two of his sons are taken captive and imprisoned in Constantinople where Leo dies shortly thereafter.
