Why did the celts hole up in place called Alesia? It was the most prominent place in the druid’s sacred geometry. In fact most of the places where the celts battled the romans were important places in their sacred geometry. The geometry didn’t help their cause.
The celts were much more of a civilization than Caesar gave them credit for. After all, traveled quickly through gaul on their roads.
There’s a book out now by Graham Robb called “The discovery of middle earth” which does a good job of telling the celts story. apparently they were a mixture of an older people in the land and some new arrivals carrying greek mythology science and culture about 600 BC.
The Romans were grossed out by the Celts human sacrifice practices and they were appalled by Caesar extermination of much of the celtic population in Gaul.
I understood the history. Less so the geometry.
Celtic roads were indifferently improved "turkey trails" that connected villages with the most convenient fords of streams; mostly they resembled the grassy lanes familiar to those of us who grew up on or near rural farmland (even the fords would be familiar), and the most maintenance they received was the continual traffic. The English tradition of "the old straight track" grew, for the most part, out of the continued use of Roman roads, which did indeed, sometimes, get built over one or more existing tracks, here and there.
The Romans introduced bridgebuilding to Britain, so they weren't concerned about the best location to ford a river or stream. By the Middle Ages the locals had quarried the Roman bridges (probably mostly in poor repair by then) out of existence, and created the "birdfoot" -- as the road started down the slopes toward the river or stream, switchbacks were used to keep the carts of the time from rolling out of control, and to reach whatever ford or crossing had come into use.
By Caesar's account, he and his army killed perhaps a million Gauls (a figure that is probably too high, but the economic disruption of the Gallic Wars may have led to that many deaths through loss of breadwinners, famine, and introduced diseases), and enslaved perhaps a further million. The Romans are, and the Roman era in Europe is, fascinating and inspirational in many ways, but the brutality of their slave-based economy grosses me out.
Graham Robb should be regarded as an entertaining speculative writer, and not much else, imho.