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
When the senate (in the spring of 704) at the suggestion of Pompeius requested both him and Caesar to furnish each a legion for the impending Parthian war(20) and when agreeably to this resolution Pompeius demanded back from Caesar the legion lent to him some years before, so as to send it to Syria, Caesar complied with the double demand, because neither the opportuneness of this decree of the senate nor the justice of the demand of Pompeius could in themselves be disputed, and the keeping within the bounds of the law and of formal loyalty was of more consequence to Caesar than a few thousand soldiers.
20. Cf. V. IX. Dictatorship of Pompeius
The two legions came without delay and placed themselves at the disposal of the government, but instead of sending them to the Euphrates, the latter kept them at Capua in readiness for Pompeius; and the public had once more the opportunity of comparing the manifest endeavours of Caesar to avoid a rupture with the perfidious preparation for war by his opponents.
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Reference address : https://www.ellopos.net/elpenor/rome/5-09-crassus-joint-rulers.asp?pg=42