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
Expeditions to Britain
There remained the insular Celts. From the close connection between them and the Celts of the continent, especially the maritime cantons, it may readily be conceived that they had at least sympathized with the national resistance, and that if they did not grant armed assistance to the patriots, they gave at any rate an honourable asylum in their sea-protected isle to every one who was no longer safe in his native land.
This certainly involved a danger, if not for the present, at any rate for the future; it seemed judicious--if not to undertake the conquest of the island itself--at any rate to conduct there also defensive operations by offensive means, and to show the islanders by a landing on the coast that the arm of the Romans reached even across the Channel.
Do you see any typos or other mistakes? Please let us know and correct them
Reference address : https://www.ellopos.net/elpenor/rome/5-07-subjugation-west.asp?pg=91