Please note that Mommsen uses the AUC chronology (Ab Urbe Condita), i.e. from the founding of the City of Rome. You can use this reference table to have the B.C. dates
From: The History of Rome, by Theodor Mommsen
Translated with the sanction of the author by William Purdie Dickson
Expedition against Parthia Resolved on
He found the Parthian war already commenced. The faithless conduct of Pompeius towards the Parthians has been already mentioned;(1) he had not respected the stipulated frontier of the Euphrates and had wrested several provinces from the Parthian empire for the benefit of Armenia, which was now a client state of Rome.
1. iv. 434
King Phraates had submitted to this treatment; but after he had been murdered by his two sons Mithradates and Orodes, the new king Mithradates immediately declared war on the king of Armenia, Artavasdes, son of the recently deceased Tigranes (about 698).(2)
2. Tigranes was still living in February 698 (Cic. pro Sest. 27, 59); on the other hand Artavasdes was already reigning before 700 (Justin, xlii. 2, 4; Plut. Crass. 49).
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Reference address : https://www.ellopos.net/elpenor/rome/5-09-crassus-joint-rulers.asp?pg=2