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
Indeed it is not improbable that this occurrence contributed materially, though not just at the moment, to diminish the antagonism between Rome and Etruria, and above all to knit more closely the ties of union between Latium and Rome. The conflict between the Gauls and the Romans was not, like that between Rome and Etruria or between Rome and Samnium, a collision of two political powers which affect and modify each other; it may be compared to those catastrophes of nature, after which the organism, if it is not destroyed, immediately resumes its equilibrium.
The Gauls often returned to Latium: as in the year 387, when Camillus defeated them at Alba--the last victory of the aged hero, who had been six times military tribune with consular powers, and five times dictator, and had four times marched in triumph to the Capitol; in the year 393, when the dictator Titus Quinctius Pennus encamped opposite to them not five miles from the city at the bridge of the Anio, but before any encounter took place the Gallic host marched onward to Campania; in the year 394, when the dictator Quintus Servilius Ahala fought in front of the Colline gate with the hordes returning from Campania; in the year 396, when the dictator Gaius Sulpicius Peticus inflicted on them a signal defeat; in the year 404, when they even spent the winter encamped upon the Alban mount and joined with the Greek pirates along the coast for plunder, till Lucius Furius Camillus, the son of the celebrated general, in the following year dislodged them--an incident which came to the ears of Aristotle who was contemporary (370-432) in Athens.
But these predatory expeditions, formidable and troublesome as they may have been, were rather incidental misfortunes than events of political significance; and their most essential result was, that the Romans were more and more regarded by themselves and by foreigners as the bulwark of the civilized nations of Italy against the onset of the dreaded barbarians--a view which tended more than is usually supposed to further their subsequent claim to universal empire.
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Reference address : https://www.ellopos.net/elpenor/rome/2-04-fall-etruscan-celts.asp?pg=26