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 position of the new supreme head of the state appears formally, at least in the first instance, as a dictatorship. Caesar took it up at first after his return from Spain in 705, but laid it down again after a few days, and waged the decisive campaign of 706 simply as consul--this was the office his tenure of which was the primary occasion for the outbreak of the civil war.(7)
7. Cf. V. IX. Preparation for Attacks on Caesar
But in the autumn of this year after the battle of Pharsalus he reverted to the dictatorship and had it repeatedly entrusted to him, at first for an undefined period, but from the 1st January 709 as an annual office, and then in January or February 710(8) for the duration of his life, so that he in the end expressly dropped the earlier reservation as to his laying down the office and gave formal expression to its tenure for life in the new title of -dictator perpetuus-.
8. On the 26th January 710 Caesar is still called dictator IIII (triumphal table); on the 18th February of this year he was already -dictator perpetuus- (Cicero, Philip, ii. 34, 87). Comp. Staatsrecht, ii. 3 716.
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Reference address : https://www.ellopos.net/elpenor/rome/5-11-old-republic-new-monarchy.asp?pg=30