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
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).