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 Celts, nevertheless, continued the struggle; the same Roman army which had conquered at Cremona was next year (555), chiefly through the fault of its careless leader, almost destroyed by the Insubres; and it was not till 556 that Placentia could be partially re-established. But the league of the cantons associated for the desperate struggle suffered from intestine discord; the Boii and Insubres quarrelled, and the Cenomani not only withdrew from the national league, but purchased their pardon from the Romans by a disgraceful betrayal of their countrymen; during a battle in which the Insubres engaged the Romans on the Mincius, the Cenomani attacked in rear, and helped to destroy, their allies and comrades in arms (557).
Thus humbled and left in the lurch, the Insubres, after the fall of Comum, likewise consented to conclude a separate peace (558). The conditions, which the Romans prescribed to the Cenomani and Insubres, were certainly harder than they had been in the habit of granting to the members of the Italian confederacy; in particular, they were careful to confirm by law the barrier of separation between Italians and Celts, and to enact that never should a member of these two Celtic tribes be capable of acquiring the citizenship of Rome.
Do you see any typos or other mistakes? Please let us know and correct them
Reference address : https://www.ellopos.net/elpenor/rome/3-07-peace-hannibal-third-period.asp?pg=2