The Romans, concerned by the threat from Tigranes' expanding empire, dispatch an army against him, Mithridates having taken refuge with his son-in-law in the new Armenian imperial capital of Tigranocerta in the Arzenene district.

Lucullus leads a campaign into Armenia against Tigranes and begins a siege of Tigranocerta.

Tigranes returns from mopping up a Seleucid rebellion in Syria with an experienced army that Lucullus nonetheless annihilates in the fierce Battle of Tigranocerta, fought on the same (pre-Julian) calendar date as the Roman disaster at Arausio thirty-six years earlier, the day before the Nones of October according to the reckoning of the time (or October 6), which is Julian October 16, 69 BCE.

Lucullus takes the rich Armenian capital; …

…Tigranes retires to the northern regions of his kingdom to gather another army and defend his hereditary capital of Artaxata, while …

…Lucullus moves off southeastwards to Corduene on the frontiers of the Armenian and Parthian empires.

Both sides open negotiations during the winter of 69-68 BCE with the Parthian king, Arsaces XVI, who is presently defending himself against a major onslaught from his rival Phraates III coming from Bactria and the far east.

Pompey, now free to plan the consolidation of the eastern provinces and frontier kingdoms, receives Tigranes graciously and for six thousand talents …

…he restores the king to the Armenian throne in exchange for Syria and other southern conquests, thereby establishing Tigranes as a friend and ally of Rome—and as his own protégé.

Tigranes continues to rule over Armenia as a Roman client-king, though he has lost all his conquests except Sophene and Corduene.

Rejecting a request by Parthian king Phraates III to recognize the Euphrates as the limit of Roman control, …

Mithridates III of Parthia, with the assistance of his brother Orodes II, murders his father Phraates III.

Orodes takes the Parthian throne; Mithridates is made king of Media and wages war against his brother, but is soon deposed on account of his cruelty.