Many people automatically assume that history will jump from one society to another, not taking into account that there already was an established religious order in Gaul at the time of conquest.

I too am interested in the discussion on Romans basing the design of their temples in Gaul on the older nemetons of Gaul. Augustus was a master at assimilating the older, Gallic rites by building over the ancient Celtic temples with the newer, shinier Roman temples. He also assumed the role of the Celts chief god, Lugh, by changing the names of areas with Lugh in them to his own. An example of this is the area of Lyon. It was originally Lugdunnum, but was changed to Augustodunnum when Augustus set the Gallo-Roman council there.

Of course the Celts did not go peacefully into Roman submission either, by the accounts of several other rebellions in Gaul in the 1st and 2nd centuries.