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
Vercingetorix, however, doubtless even while
he was confronting Caesar on the Allier, had caused sufficient
stores to be collected in Gergovia and a fixed camp provided
with strong stone ramparts to be constructed for his troops in front
of the walls of the town, which was situated on the summit of a pretty
steep hill; and, as he had a sufficient start, he arrived before
Caesar at Gergovia and awaited the attack in the fortified camp
under the wall of the fortress.
Caesar with his comparatively
weak army could neither regularly besiege the place nor even
sufficiently blockade it; he pitched his camp below the rising
ground occupied by Vercingetorix, and was compelled to preserve
an attitude as inactive as his opponent. It was almost a victory
for the insurgents, that Caesar's career of advance from triumph
to triumph had been suddenly checked on the Seine as on the Allier.
In fact the consequences of this check for Caesar were almost
equivalent to those of a defeat.