CHOSROES, called by Dio Cassius OSROES,
a younger son of Vologeses I., succeeded his brother Pacorus during the reign of Trajan. Soon
after his accession, he invaded Armenia, expelled Exedares, the son of Tiridates, who had been
appointed king by the Romans, and gave the crown to his nephew Parthamasiris, the son of his
brother Pacorus. Trajan hastened in person to the east, conquered Armenia, and reduced it to
the form of a Roman province. Parthamasiris also fell into his hands. After concluding peace
with Augarus, the ruler of Edessa, Trajan overran the northern part of Mesopotamia, took
Nisibis land several other cities, and, after a most glorious campaign, returned to Antioch to
winter, A. D. 114. In consequence of these successes, he received the
surname of Parthicus from the soldiers and of Optimus from the senate. Parthia was at this time torn by civil commotions, which
rendered the conquests of Trajan all the easier. In the spring of the following year, A. D. 115, he crossed the Tigris, took Ctesiphon and Seleuceia, and made
Mesopotamia, Assyria, and Babylonia, Roman provinces. After these conquests, he sailed down
the Tigris to the Persian gulf and the Indian ocean; but during his absence there was a
general revolt of the Parthians. He immediately sent against them two of his generals, Maximus
and Lusius, A. D. 116, the former of whom was defeated and slain by
Chosroes, but the latter met with more success, and regained the cities of Nisibis, Edessa,
and Seleuceia, as well as others which had revolted. Upon his return to Ctesiphon, Trajan
appointed Parthamaspates king of Parthia, and then withdrew from the country to invade Arabia.
Upon the death of Trajan, however, in the following year (A. D. 117),
the Parthians expelled Parthanmaspates, and placed upon the throne their former king,
Chosroes. But Hadrian, who had succeeded Trajan, was unwilling to engage in a war with the
Parthians, and judged it more prudent to give up the conquests which Trajan had gained; he
accordingly withdrew the Roman garrisons from Mesopotamia, Assyria, and Babylonia, and made
the Euphrates, as before, the eastern boundary of the Roman empire. The exact time of
Chosroes' death is unknown; but during the remainder of his reign there was no war between the
Parthians and the Romans, as Hadrian cultivated friendly relations with the former. (Dio Cass.
ixviii. 17-33; Aurel. Vict. Caes. 100.13 ; Paus.
5.12.4; Spartian, Hadr. 100.21.)