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
Neoptolemus defeated them at the straits of Panticapaeum partly by water, partly in winter on the ice; Chersonesus was delivered, the strongholds of the Taurians were broken, and the possession of the peninsula was secured by judiciously constructed fortresses. Diophantus marched against the Reuxinales or, as they were afterwards called, the Roxolani (between the Dnieper and Don) who came forward to the aid of the Taurians; 50,000 of them fled before his 6000 phalangites, and the Pontic arms penetrated as far as the Dnieper.(7)
7. The recently discovered decree of the town of Chersonesus in honour of this Diophantus (Dittenberger, Syll. n. 252) thoroughly confirms the traditional account. It shows us the city in the immediate vicinity--the port of Balaclava must at that time have been in the power of the Tauri and Simferopol in that of the Scythians--hard pressed partly by the Tauri on the south coast of the Crimea, partly and especially by the Scythians who held in their power the whole interior of the peninsula and the mainland adjoining; it shows us further how the general of king Mithradates relieves on all sides the Greek city, defeats the Tauri, and erects in their territory a stronghold (probably Eupatorion), restores the connection between the western and the eastern Hellenes of the peninsula, overpowers in the west the dynasty of Scilurus, and in the east Saumacus prince of the Scythians, pursues the Scythians even to the mainland, and at length conquers them with the Reuxinales--such is the name given to the later Roxolani here, where they first appear--in the great pitched battle, which is mentioned also in the traditional account.
There does not seem to have been any formal subordination of the Greek city under the king; Mithradates appears only as protecting ally, who fights the battles against the Scythians that passed as invincible (--tous anupostatous dokountas eimen--), on behalf of the Greek city, which probably stood to him nearly in the relation of Massilia and Athens to Rome. The Scythians on the other band in the Crimea become subjects (--upakooi--) of Mithradates.
Thus Mithradates acquired here a second kingdom combined with that of Pontus and, like the latter, mainly based on a number of Greek commercial towns. It was called the kingdom of the Bosporus; it embraced the modern Crimea with the opposite Asiatic promontory, and annually furnished to the royal chests and magazines 200 talents (48,000 pounds) and 270,000 bushels of grain. The tribes of the steppe themselves from the north slope of the Caucasus to the mouth of the Danube entered, at least in great part, into relations of dependence on, or treaty with, the Pontic king and, if they furnished him with no other aid, afforded at any rate an inexhaustible field for recruiting his armies.
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Reference address : https://www.ellopos.net/elpenor/rome/4-08-east-king-mithradates.asp?pg=21