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
Pompeius Goes to Brundisium - Embarkation for Greece
Pompeius had given up Italy as lost, so soon as Caesar had occupied Picenum; only he wished to delay his embarkation as long as possible, with the view of saving so much of his force as could still be saved. Accordingly he had slowly put himself in motion for the nearest seaport Brundisium. Thither came the two legions of Luceria and such recruits as Pompeius had been able hastily to collect in the deserted Apulia, as well as the troops raised by the consuls and other commissioners in Campania and conducted in all haste to Brundisium; thither too resorted a number of political fugitives, including the most respected of the senators accompanied by their families.
The embarkation began; but the vessels at hand did not suffice to transport all at once the whole multitude, which still amounted to 25,000 persons. No course remained but to divide the army. The larger half went first (4 March); with the smaller division of some 10,000 men Pompeius awaited at Brundisium the return of the fleet; for, however desirable the possession of Brundisium might be for an eventual attempt to reoccupy Italy, they did not presume to hold the place permanently against Caesar. Meanwhile Caesar arrived before Brundisium; the siege began.
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Reference address : https://www.ellopos.net/elpenor/rome/5-10-brundisium-pharsalus-thapsus.asp?pg=25