Flavius Josephus, Antiquities of the Jews
William Whiston, A.M., Ed.

[39] About this time died Phraates, king of the Parthians, by the treachery of Phraataces his son, upon the occasion following: When Phraates had had legitimate sons of his own, he had also an Italian maid-servant, whose name was Thermusa, who had been formerly sent to him by Julius Caesar, among other presents. He first made her his concubine; but he being a great admirer of her beauty, in process of time having a son by her, whose name was Phraataces, he made her his legitimate wife, and had a great respect for her. Now she was able to persuade him to do any thing that she said, and was earnest in procuring the government of Parthia for her son; but still she saw that her endeavors would not succeed, unless she could contrive how to remove Phraates's legitimate sons [out of the kingdom;] so she persuaded him to send those his sons as pledges of his fidelity to Rome; and they were sent to Rome accordingly, because it was not easy for him to contradict her commands. Now while Phraataces was alone brought up in order to succeed in the government, he thought it very tedious to expect that government by his father's donation [as his successor]; he therefore formed a treacherous design against his father, by his mother's assistance, with whom, as the report went, he had criminal conversation also. So he was hated for both these vices, while his subjects esteemed this [wicked] love of his mother to be no way inferior to his parricide; and he was by them, in a sedition, expelled out of the country before he grew too great, and died. But as the best sort of Parthians agreed together that it was impossible they should be governed without a king, while also it was their constant practice to choose one of the family of Arsaces, [nor did their law allow of any others; and they thought this kingdom had been sufficiently injured already by the marriage with an Italian concubine, and by her issue,] they sent ambassadors, and called Orodes [to take the crown]; for the multitude would not otherwise have borne them; and though he was accused of very great cruelty, and was of an untractable temper, and prone to wrath, yet still he was one of the family of Arsaces. However, they made a conspiracy against him, and slew him, and that, as some say, at a festival, and among their sacrifices; (for it is the universal custom there to carry their swords with them;) but, as the more general report is, they slew him when they had drawn him out a hunting. So they sent ambassadors to Rome, and desired they would send one of those that were there as pledges to be their king. Accordingly, Vonones was preferred before the rest, and sent to them (for he seemed capable of such great fortune, which two of the greatest kingdoms under the sun now offered him, his own and a foreign one). However, the barbarians soon changed their minds, they being naturally of a mutable disposition, upon the supposal that this man was not worthy to be their governor; for they could not think of obeying the commands of one that had been a slave, (for so they called those that had been hostages,) nor could they bear the ignominy of that name; and this was the more intolerable, because then the Parthians must have such a king set over them, not by right of war, but in time of peace. So they presently invited Artabanus, king of Media, to be their king, he being also of the race of Arsaces. Artabanus complied with the offer that was made him, and came to them with an army. So Vonones met him; and at first the multitude of the Parthians stood on this side, and he put his army in array; but Artabanus was beaten, and fled to the mountains of Media. Yet did he a little after gather a great army together, and fought with Vonones, and beat him; whereupon Vonones fled away on horseback, with a few of his attendants about him, to Seleucia [upon Tigris]. So when Artabanus had slain a great number, and this after he had gotten the victory by reason of the very great dismay the barbarians were in, he retired to Ctesiphon with a great number of his people; and so he now reigned over the Parthians. But Vonones fled away to Armenia; and as soon as he came thither, he had an inclination to have the government of the country given him, and sent ambassadors to Rome [for that purpose]. But because Tiberius refused it him, and because he wanted courage, and because the Parthian king threatened him, and sent ambassadors to him to denounce war against him if he proceeded, and because he had no way to take to regain any other kingdom, (for the people of authority among the Armenians about Niphates joined themselves to Artabanus,) he delivered up himself to Silanus, the president of Syria, who, out of regard to his education at Rome, kept him in Syria, while Artabanus gave Armenia to Orodes, one of his own sons.