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
The Victory of Monarchy
The struggle, which Pompeius and the republicans had undertaken against the monarchy of Caesar, thus terminated, after having lasted for four years, in the complete victory of the new monarch. No doubt the monarchy was not established for the first time on the battle-fields of Pharsalus and Thapsus; it might already be dated from the moment when Pompeius and Caesar in league had established their joint rule and overthrown the previous aristocratic constitution.
Yet it was only those baptisms of blood of the ninth August 706 and the sixth April 708 that set aside the conjoint rule so opposed to the nature of absolute dominion, and conferred fixed status and formal recognition on the new monarchy. Risings of pretenders and republican conspiracies might ensue and provoke new commotions, perhaps even new revolutions and restorations; but the continuity of the free republic that had been uninterrupted for five hundred years was broken through, and monarchy was established throughout the range of the wide Roman empire by the legitimacy of accomplished fact.
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Reference address : https://www.ellopos.net/elpenor/rome/5-10-brundisium-pharsalus-thapsus.asp?pg=135