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 Legions of Pompeius
While Pompeius thus treated the political aspect of his position with his characteristic perversity, and did his best to make what was already bad in itself still worse, he devoted himself on the other hand with commendable zeal to his duty of giving military organization to the considerable but scattered forces of his party. The flower of his force was composed of the troops brought with him from Italy, out of which with the supplementary aid of the Illyrian prisoners of war and the Romans domiciled in Greece five legions in all were formed. Three others came from the east--the two Syrian legions formed from the remains of the army of Crassus, and one made up out of the two weak legions hitherto stationed in Cilicia.
Nothing stood in the way of the withdrawal of these corps of occupation: because on the one hand the Pompeians had an understanding with the Parthians, and might even have had an alliance with them if Pompeius had not indignantly refused to pay them the price which they demanded for it--the cession of the Syrian province added by himself to the empire; and on the other hand Caesar's plan of despatching two legions to Syria, and inducing the Jews once more to take up arms by means of the prince Aristobulus kept a prisoner in Rome, was frustrated partly by other causes, partly by the death of Aristobulus.
New legions were moreover raised-- one from the veteran soldiers settled in Crete and Macedonia, two from the Romans of Asia Minor. To all these fell to be added 2000 volunteers, who were derived from the remains of the Spanish select corps and other similar sources; and, lastly, the contingents of the subjects. Pompeius like Caesar had disdained to make requisitions of infantry from them; only the Epirot, Aetolian, and Thracian militia were called out to guard the coast, and moreover 3000 archers from Greece and Asia Minor and 1200 slingers were taken up as light troops.
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Reference address : https://www.ellopos.net/elpenor/rome/5-10-brundisium-pharsalus-thapsus.asp?pg=62