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
With unimpaired courage and increased resentment the Numantines resumed the struggle; Laenas fought against them unsuccessfully, nor was his successor Gaius Hostilius Mancinus more fortunate (617). But the catastrophe was brought about not so much by the arms of the Numantines, as by the lax and wretched military discipline of the Roman generals and by--what was its natural consequence--the annually- increasing dissoluteness, insubordination, and cowardice of the Roman soldiers. The mere rumour, which moreover was false, that the Cantabri and Vaccaei were advancing to the relief of Numantia, induced the Roman army to evacuate the camp by night without orders, and to seek shelter in the entrenchments constructed sixteen years before by Nobilior.(5)
5. Cf. IV. I. Celtiberian War
The Numantines, informed of their sudden departure, hotly pursued the fugitive army, and surrounded it: there remained to it no choice save to fight its way with sword in hand through the enemy, or to conclude peace on the terms laid down by the Numantines. Although the consul was personally a man of honour, he was weak and little known. Tiberius Gracchus, who served in the army as quaestor, had more influence with the Celtiberians from the hereditary respect in which he was held on account of his father who had so wisely organized the province of the Ebro, and induced the Numantines to be content with an equitable treaty of peace sworn to by all the staff-officers.
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Reference address : https://www.ellopos.net/elpenor/rome/4-01-gracchi.asp?pg=21