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
Their equipment and style of fighting were consonant to this mode of life; the inhabitants of these steppes fought in great measure on horseback and always in loose array, equipped with helmet and coat of mail of leather and leather-covered shield, armed with sword, lance, and bow--the ancestors of the modern Cossacks.
The Scythians originally settled there, who seem to have been of Mongolian race and akin in their habits and physical appearance to the present inhabitants of Siberia, had been followed up by Sarmatian tribes advancing from east to west,--Sauromatae, Roxolani, Jazyges,--who are commonly reckoned of Slavonian descent, although the proper names, which we are entitled to ascribe to them, show more affinity with Median and Persian names and those peoples perhaps belonged rather to the great Zend stock.
Thracian tribes moved in the opposite direction, particularly the Getae, who reached as far as the Dniester. Between the two there intruded themselves--probably as offsets of the great Germanic migration, the main body of which seems not to have touched the Black Sea--the Celts, as they were called, on the Dnieper, the Bastarnae in the same quarter, and the Peucini at the mouth of the Danube. A state, in the proper sense, was nowhere formed; every tribe lived by itself under its princes and elders.
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Reference address : https://www.ellopos.net/elpenor/rome/4-08-east-king-mithradates.asp?pg=16