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
New Aggressions of Mithradates
So it was alleged; but in fact there was little trace of any real return of the former order of things. Scarce had Sulla left Asia, when Tigranes king of Great Armenia fell upon Ariobarzanes the new king of Cappadocia, expelled him, and reinstated in his stead the Pontic pretender Ariarathes. In Bithynia, where after the death of the old king Nicomedes II (about 663) his son Nicomedes III Philopator had been recognized by the people and by the Roman senate as legitimate king, his younger brother Socrates came forward as pretender to the crown and possessed himself of the sovereignty.
It was clear that the real author of the Cappadocian as of the Bithynian troubles was no other than Mithradates, although he refrained from taking any open part. Every one knew that Tigranes only acted at his beck; but Socrates also had marched into Bithynia with Pontic troops, and the legitimate king's life was threatened by the assassins of Mithradates. In the Crimea even and the neighbouring countries the Pontic king had no thought of receding, but on the contrary carried his arms farther and farther.
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Reference address : https://www.ellopos.net/elpenor/rome/4-08-east-king-mithradates.asp?pg=31