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
But when Caesar's legions saw in the gray morning the enemy's columns which had been retiring since midnight, they discerned with the sure instinct of experienced veterans the strategic importance of this retreat, which would compel them to follow their antagonists into distant and impracticable regions filled by hostile troops; at their own request the general ventured to lead the infantry also into the river, and although the water reached up to the shoulders of the men, it was crossed without accident. It was high time. If the narrow plain, which separated the town of Ilerda from the mountains enclosing the Ebro were once traversed and the army of the Pompeians entered the mountains, their retreat to the Ebro could no longer be prevented.
Already they had, notwithstanding the constant attacks of the enemy's cavalry which greatly delayed their march, approached within five miles of the mountains, when they, having been on the march since midnight and unspeakably exhausted, abandoned their original plan of traversing the whole plain on the same day, and pitched their camp. Here the infantry of Caesar overtook them and encamped opposite to them in the evening and during the night, as the nocturnal march which the Pompeians had at first contemplated was abandoned from fear of the night-attacks of the cavalry. On the following day also both armies remained immoveable, occupied only in reconnoitering the country.
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Reference address : http://www.ellopos.net/elpenor/rome/5-10-brundisium-pharsalus-thapsus.asp?pg=41