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
The Helvetian War
These troops he united with the corps stationed at Genava, and crossed the Rhone with his whole force. His unexpected appearance in the territory of the Haedui naturally at once restored the Roman party there to power, which was not unimportant as regarded supplies. He found the Helvetii employed in crossing the Saone, and moving from the territory of the Sequani into that of the Haedui; those of them that were still on the left bank of the Saone, especially the corps of the Tigorini, were caught and destroyed by the Romans rapidly advancing.
The bulk of the expedition, however, had already crossed to the right bank of the river; Caesar followed them and in twenty-four hours effected the passage, which the unwieldy host of the Helvetii had not been able to accomplish in twenty days. The Helvetii, prevented by this passage of the river on the part of the Roman army from continuing their march westward, turned in a northerly direction, doubtless under the supposition that Caesar would not venture to follow them far into the interior of Gaul, and with the intention, if he should desist from following them, of turning again toward their proper destination.
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Reference address : https://www.ellopos.net/elpenor/rome/5-07-subjugation-west.asp?pg=62