Lysandros PM'd me about Quintus Labienus. He was the ambassador to the parthians and after Caesar was murdered and Brutus and Cassius defeated (whose side he took) he defected to the Parthians. He then led a sizeable roman-parthian army and took pretty much all of Asia Minor, but was killed a year later by a roman counterattack. http://en.wikipedia.org/wiki/Quintus_Labienus

Does anyone know much about the army composition? Were many of those soldiers romans? I know it's not in italy, but this discussion of romans refusing to serve in other armies might be enlightened with more information on this event.