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
Caesar on the Right Bank of the Rhine
Caesar however found it advisable to take yet a further step and to lead the legions over the Rhine. He was not without connections beyond the river. the Germans at the stage of culture which they had then reached, lacked as yet any national coherence; in political distraction they--though from other causes--fell nothing short of the Celts. The Ubii (on the Sieg and Lahn), the most civilized among the German tribes, had recently been made subject and tributary by a powerful Suebian canton of the interior, and had as early as 697 through their envoys entreated Caesar to free them like the Gauls from the Suebian rule.
It was not Caesar's design seriously to respond to this suggestion, which would have involved him in endless enterprises; but it seemed advisable, with the view of preventing the appearance of the Germanic arms on the south of the Rhine, at least to show the Roman arms beyond it. The protection which the fugitive Usipetes and Tencteri had found among the Sugambri afforded a suitable occasion. In the region, apparently between Coblentz and Andernach, Caesar erected a bridge of piles over the Rhine and led his legions across from the Treverian to the Ubian territory.
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Reference address : https://www.ellopos.net/elpenor/rome/5-07-subjugation-west.asp?pg=89