When he came to the throne in 70 BC, the Roman general Lucullus was preparing to attack Tigranes the Great, king of Armenia, who was supreme in western Asia and had wrested Mesopotamia and several vassal states from Parthia. Naturally, Phraates declined to assist Mithradates VI of Pontus and Tigranes against the Romans. Instead, he supported his son-in-law, the younger Tigranes, when he rebelled against his father, and invaded Armenia in 65 BC in alliance with Pompey, who abandoned Mesopotamia to the Parthians. But Pompey soon overrode the treaty; he acknowledged the elder Tigranes, took his son prisoner, occupied the vassal states Gordyene and Osroene for the Romans, and denied the title of "king of kings," which Phraates had adopted again, to the Parthian king. About 57 BC Phraates was murdered by his two sons, Orodes II and Mithridates III.
