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 the attacked offered valiant resistance, and, as the ground on which the fight took place had been several times employed for the encampment of larger and lesser divisions and was intersected in various directions by mounds and ditches, Caesar's right wing along with the cavalry entirely missed its way; instead of supporting the left in attacking the Pompeian legion, it got into a narrow trench that led from one of the old camps towards the river.
So Pompeius, who came up in all haste with five legions to the aid of his troops, found the two wings of the enemy separated from each other, and one of them in an utterly forlorn position. When the Caesarians saw him advance, a panic seized them; the whole plunged into disorderly flight; and, if the matter ended with the loss of 1000 of the best soldiers and Caesar's army did not sustain a complete defeat, this was due simply to the circumstance that Pompeius also could not freely develop his force on the broken ground, and to the further fact that, fearing a stratagem, he at first held back his troops.
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Reference address : https://www.ellopos.net/elpenor/rome/5-10-brundisium-pharsalus-thapsus.asp?pg=75