At its height, his empire extended from the Pontic Alps (in modern north-eastern Turkey) to Mesopotamia, and from the Caspian Sea to the Mediterranean. A series of victories led him to assume the Achaemenid title of King of Kings, which even the Parthian kings did not assume, appearing on coins struck after 85 BC. He was called "Tigranes the Great" by many Western historians and writers, such as Plutarch. The "King of Kings" never appeared in public without having four kings attending him. Cicero, referring to his success in the east, said that he "made the Republic of Rome tremble before the prowess of his arms."