Musa was the beautiful concubine sent by the emperor Augustus to Phraates IV in appreciation for the return of the military standards lost by Crassus.
Josephus relates her story in Antiquities of the Jews (XVIII.2.4). A royal favorite, she gave birth to Phraataces. Determined that he succeed to the Parthian throne, she persuaded Phraates to send his own sons to Rome as hostages and then poisoned him. Proclaimed king, Musa then married Phraataces.
And so this former Roman slave became queen of Parthia.