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
Especially among the Celtic nobility there prevailed an excitement, which seemed every moment as if it must break out into a general insurrection. Even before the second expedition to Britain in the spring of 700 Caesar had found it necessary to go in person to the Treveri, who, since they had compromised themselves in the Nervian conflict in 697, had no longer appeared at the general diets and had formed more than suspicious connections with the Germans beyond the Rhine. At that time Caesar had contented himself with carrying the men of most note among the patriot party, particularly Indutiomarus, along with him to Britain in the ranks of the Treverian cavalry-contingent; he did his utmost to overlook the conspiracy, that he might not by strict measures ripen it into insurrection.
But when the Haeduan Dumnorix, who likewise was present in the army destined for Britain, nominally as a cavalry officer, but really as a hostage, peremptorily refused to embark and rode home instead, Caesar could not do otherwise than have him pursued as a deserter; he was accordingly overtaken by the division sent after him and, when he stood on his defence, was cut down (700). That the most esteemed knight of the most powerful and still the least dependent of the Celtic cantons should have been put to death by the Romans, was a thunder-clap for the whole Celtic nobility; every one who was conscious of similar sentiments--and they formed the great majority-- saw in that catastrophe the picture of what was in store for himself.
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=97