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
It was no wonder that what took place after the victories of Metellus was repeated on a greater scale after the defeats of Gnaeus Mallius and Quintus Caepio. Once more Gaius Marius came forward, in spite of the law which prohibited the holding of the consulship more than once, as a candidate for the supreme magistracy; and not only was he nominated as consul and charged with the chief command in the Gallic war, while he was still in Africa at the head of the army there, but he was reinvested with the consulship for five years in succession (650-654)--in a way, which looked like an intentional mockery of the exclusive spirit that the nobility had exhibited in reference to this very man in all its folly and shortsightedness, but was also unparalleled in the annals of the republic, and in fact absolutely incompatible with the spirit of the free constitution of Rome.
In the Roman military system in particular--the transformation of which from a burgess-militia into a body of mercenaries, begun in the African war, was continued and completed by Marius during his five years of a supreme command unlimited through the exigencies of the time still more than through the terms of his appointment--the profound traces of this unconstitutional commandership-in-chief of the first democratic general remained visible for all time.
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Reference address : https://www.ellopos.net/elpenor/rome/4-05-peoples-north.asp?pg=41