3. Q.Labienus, the son of the preceding, joined the party of Brutus and Cassius after the murder of Caesar (B. C. 44), and was sent by them into Parthia to seek aid from Orodes, the Parthian king. [ARSACES XIV.] Here he remained for a considerable time, and before he could obtain any definite answer from Orodes, the news came of the battle of Philippi (B. C. 42). Seeing that the triumvirs were resolved to spare none of their opponents, Labienus made up his mind to continue in Parthia; but circumstances soon occurred which enabled him to take revenge upon the victorious party. The attention of Octavian was filly engaged by the affairs of Italy and the war against Sex. Pompey; and Antony, to whom the government of the East had devolved, had retired to Egypt, captivated by the charms of Cleopatra, and careless about every thing else. Labienus persuaded Orodes to embrace this favourable opportunity for the invasion of the Roman provinces in Asia; and accordingly the Parthian king entrusted to him and Pacorus a large army for the purpose. They crossed the Euphrates, and invaded Syria, in B. C. 40. At first they were repulsed from the walls of Apameia; but as almost all the fortified places were garrisoned by the old soldiers of Brutus and Cassius, who had joined the army of the triumvirs after the victory of the latter, Labienus and Pacorus met with little resistance. Most of these troops joined their banners ; but their commander, Decidius Saxa, continued firm in his allegiance to Antony. He was, however, easily overcome in battle; and as the fruit of this victory, Labienus and the Parthians obtained possession of the two great towns of Antioch and Apameia, While Pacorus remained with the Parthians in Syria, to complete the subjugation of the country, advancing for that object as far south as Palestine, Labienus, with the Roman troops he had collected, entered Asia Minor in pursuit of Saxa, whom he overtook and slew in Cilicia, and then proceeded along the south of Asia Minor, receiving the submission of almost all the cities in his way. The only resistance he experienced was from Alabanda, Mylasa, and Stratoniceia; the two former of which he took by force [compare HYBREAS], while the latter successfully resisted all his efforts. Hereupon he assumed the name of Parthian imperator, a title which we also find upon his coins, as is mentioned below. In adopting this title, Dio Cassius remarks (48.26), Labienus departed from the custom of all Roman commanders, who were wont to take such titles from the names of the people whom they conquered, of which we have examples in Scipio Africanus, Servilius Isauricus, Fabius Allobrogicus, and the like, while Labienus, on the contrary, assumed his from the victorious nation. It was in reference to this that Hybreas, when he was defending Mylasus, sent Labienus the taunting message that he would call himself the Carian imperator.

These successes at length roused Antony from his inactivity. He sent an army into Asia Minor in B. C. 39, commanded by P. Ventidius, the most able of his legates, who suddenly came upon Labienus before the latter had received any intelligence of his approach. Not having any of his Parthian allies with him, he dared not meet Ventidius in the field, and, accordingly, fled with the utmost haste towards Syria, to effect a junction with Pacorus. This, however, was prevented by the rapid pursuit of Ventidius, who came up with him by Mount Taurus, and stopped him from advancing further. Here both parties remained for some days, Ventidius waiting for his heavy-armed troops, and Labienus the arrival of the Parthians. The latter marched to his assistance, but were defeated by Ventidius before they joined Labienus, whom they then deserted, and fled into Cilicia. In these circumstances Labienus, not daring to engage with Ventidius, abandoned his men, and fled in disguise into Cilicia. Here he remained concealed for some time, but was at length apprehended by Demetrius, a freedman of Octavian, and put to death. It would appear, from a statement of Strabo (xiv. p.600), that this Labienus possessed the same arrogance and vehemence of temper which distinguished his father. (D. C. 48.24-26, 39, 40; Liv. Epit. cxxvii.; Flor. 4.9 ; Vell. 2.78; Plut. Ant. 30, 33; Appian, App. BC 5.65, 133; Justin, 42.4.) The coin annexed has on the obverse the head of Labienus, with the legend Q. LABIENVS PARTHICVS IMP., and on the reverse a horse, which refers clearly to the celebrated cavalry of the Parthians. (Eckhel, vol. v. p. 146.)