Here is a little secret about the Celts. There are no Celts. Never were. There were just a bunch of tribes. The Iverni and the Iceni, and the Brigantes, and the Silurans and on and on! No Celt saw themselves as a Celt, they just saw their tribe. read more
The Druids were a cult that was a danger to Roman intentions in Britain. They did the same thing with the Christians and eliminated the threat at the source. This slaughter of the druids actually had consequences. Boadicea, queen of the Iceni tribe, plotted revenge and this was one of the reasons to the battle of Watling Street. read more
The Romans had met the Druids before in conquered Western Europe. While the Romans were happy to make a peaceful settlement with most tribes/groups in England, they had no intention of doing the same with the Druids. The Druids were priests. The Britons both respected and feared them. read more
Furthermore, the Romans didn't slaughter them. The Romans conquered some of the Celtic lands and treated them like other conquered people: they were pretty hands off so long as the Celts behaved. The Druids remained in Britain long past the fall of the Roman Empire. read more