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
They then took up a position at Ilerda (Lerida) between the Pyrenees and the Ebro. This town lies twenty miles to the north of the Ebro on the right bank of one of its tributaries, the Sicoris (Segre), which was crossed by only a single solid bridge immediately at Ilerda. To the south of Ilerda the mountains which adjoin the left bank of the Ebro approach pretty close to the town; to the northward there stretches on both sides of the Sicoris a level country which is commanded by the hill on which the town is built.
For an army, which had to submit to a siege, it was an excellent position; but the defence of Spain, after the occupation of the line of the Pyrenees had been neglected, could only be undertaken in earnest behind the Ebro, and, as no secure communication was established between Ilerda and the Ebro, and no bridge existed over the latter stream, the retreat from the temporary to the true defensive position was not sufficiently secured.
The Caesarians established themselves above Ilerda, in the delta which the river Sicoris forms with the Cinga (Cinca), which unites with it below Ilerda; but the attack only began in earnest after Caesar had arrived in the camp (23 June). Under the walls of the town the struggle was maintained with equal exasperation and equal valour on both sides, and with frequent alternations of success; but the Caesarians did not attain their object-- which was, to establish themselves between the Pompeian camp and the town and thereby to possess themselves of the stone bridge-- and they consequently remained dependent for their communication with Gaul solely on two bridges which they had hastily constructed over the Sicoris, and that indeed, as the river at Ilerda itself was too considerable to be bridged over, about eighteen or twenty miles farther up.
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Reference address : https://www.ellopos.net/elpenor/rome/5-10-brundisium-pharsalus-thapsus.asp?pg=37