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
It was more than a great victory; the fate of Alesia, and indeed of the Celtic nation, was thereby irrevocably decided. The Celtic army, utterly disheartened, dispersed at once from the battle-field and went home. Vercingetorix might perhaps have even now taken to flight, or at least have saved himself by the last means open to a free man; he did not do so, but declared in a council of war that, since he had not succeeded in breaking off the alien yoke, he was ready to give himself up as a victim and to avert as far as possible destruction from the nation by bringing it on his own head. This was done.
The Celtic officers delivered their general-- the solemn choice of the whole nation--over to the energy of their country for such punishment as might be thought fit. Mounted on his steed and in full armour the king of the Arverni appeared before the Roman proconsul and rode round his tribunal; then he surrendered his horse and arms, and sat down in silence on the steps at Caesar's feet (702).
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Reference address : https://www.ellopos.net/elpenor/rome/5-07-subjugation-west.asp?pg=129