at the time [Julius Caesar's rise] "Gaul" was basically a more Germanic country, and it was the Roman conquest, which created a "Franco-Gallic" culture, which in the end became a Latinate France. Had this not happened, France might now be "Germanic" or France and Germany might now be one country. And Rome might have turned eastward, or rather not have been pulled westward, and "western civilization" as we now know it might not exist.
So many turning points in history when things might have turned out so very differently!
Here are a few other historical novels featuring druids:
Morgan Llywelyn, Druids - also about Vercingetorix
Morgan Llywelyn, The Greener Shore - sequel to the above
Kate Horsley, Confessions of a Pagan Nun - see review
Marion Zimmer Bradley and Diana Paxson, The Forest House (a prequel to Mists of Avalon)