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
Expeditins against the Morini and Menapii
The Morini and Menapii alone persevered in withholding their recognition of the Roman supremacy. To compel them to this, Caesar appeared on their borders; but, rendered wiser by the experiences of their countrymen, they avoided accepting battle on the borders of their land, and retired into the forests which then stretched almost without interruption from the Ardennes towards the German Ocean. The Romans attempted to make a road through the forest with the axe, ranging the felled trees on each side as a barricade against the enemy's attacks; but even Caesar, daring as he was, found it advisable after some days of most laborious marching, especially as it was verging towards winter, to order a retreat, although but a small portion of the Morini had submitted and the powerful Menapii had not been reached at all.
In the following year (699) while Caesar himself was employed in Britain the greater part of the army was sent afresh against these tribes; but this expedition also remained in the main unsuccessful. Nevertheless the result of the last campaigns was the almost complete reduction of Gaul under the dominion of the Romans. While central Gaul had submitted to it without resistance, during the campaign of 697 the Belgic, and during that of the following year the maritime, cantons had been compelled by force of arms to acknowledge the Roman rule. The lofty hopes, with which the Celtic patriots had begun the last campaign, had nowhere been fulfilled. Neither Germans nor Britons had come to their aid; and in Belgica the presence of Labienus had sufficed to prevent the renewal of the conflicts of the previous year.
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Reference address : https://www.ellopos.net/elpenor/rome/5-07-subjugation-west.asp?pg=84