III. Roman period; from B. C. 53, to A. D. 226; comprising the wars with Rome. Arsaces XIV. (Orodes I.) _d._ 36. In his reign the first war with Rome, caused by the invasion of Crassus; it ends in the annihilation of the invading army and general, 53. In consequence of this victory the Parthians acquired such preponderance, that during the civil wars they were frequently masters on this side of the Euphrates, and in 52-51 proceeded to attack Syria.--In the war between Pompey and Caesar they sided with the former, and thus furnished the latter with a pretext for his Parthian expedition, which, however, was prevented by his murder in 44; again in the war between the triumviri and Brutus and Cassius, 42, they took the republican side. After the defeat of Brutus and Cassius, the Parthians, at the instigation of the Roman general and ambassador Labienus, and commanded by him and Pacorus, (eldest son to Arsaces,) spread over the whole of Syria and Asia Minor, 40; but, after violent exertions, were driven back by Ventidius, Antony's general, 39, 38; Pacorus lost his life, and his father died of grief. Arsaces XV. (Phraates IV.) _d._ A. D. 4, contemporary of Augustus. He confirmed his power by murdering his brothers and their dependents; his views were likewise furthered by the failure of Antony's expedition, B. C. 36, which ended pretty nearly in the same manner as that of Crassus. The remainder of his reign was disturbed by a pretender to the throne, Tiridates, who, after his defeat, 25, found an asylum at the court of Augustus. The threatened attack of Augustus was diverted by Phraates's restoration of the standards taken from Crassus, 20; a dispute, however, subsequently arose respecting the possession of the Armenian throne, A. D. 2, on which account Caius Caesar was despatched into Asia, and accommodated matters by a treaty. The ultimate fate both of the king and the empire was principally decided by a female slave, Thermusa, sent as a present from Augustus; this woman, wishing to ensure the succession to her own son, prevailed upon the king to send his four sons to Rome as hostages, under the pretext of anticipating domestic troubles, 18.--A practice which from that time became frequent, the Parthian kings thinking it a convenient mode of ridding themselves of dangerous competitors, while the Romans knew how to make the proper use of them.--Thermusa's son having grown up, she removed the king, and seated Phraataces on the throne, under the name of Arsaces XVI; he was, however, put to death by the Parthians, A. D. 4; and the crown given to one of the Arsacidae, Orodes II, (Arsaces XVII.) who was, however, immediately afterwards slain by reason of his cruelty. In consequence, Vonones I. the eldest of the sons of Phraates sent to Rome, was called back and placed on the throne (Arsaces XVIII.); but that prince having brought with him Roman