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
Such was the internal condition of the Celtic nation. It remains
that we set forth their external relations with their neighbours,
and describe the part which they sustained at this moment in the mighty
rival race and rival struggle of the nations, in which it is
everywhere still more difficult to maintain than to acquire.
Along the Pyrenees the relations of the peoples had for long been
peaceably settled, and the times had long gone by when the Celts
there pressed hard on, and to some extent supplanted, the Iberian,
that is, the Basque, original population.
The valleys of the Pyrenees
as well as the mountains of Bearn and Gascony, and also the coast-
steppes to the south of the Garonne, were at the time of Caesar
in the undisputed possession of the Aquitani, a great number
of small tribes of Iberian descent, coming little into contact
with each other and still less with the outer world; in this quarter
only the mouth of the Garonne with the important port of Burdigala
(Bordeaux) was in the hands of a Celtic tribe, the Bituriges-Vivisci.