I had always thought that Druids were ancient magicians: Merlin and his group of men skulking in the shadowy forest. But Graham Robb, in his book The Discovery of Middle Earth: Mapping the Lost World of the Celts, has described a surprisingly sophisticated culture.
Here's the historical snapshot: "Fifty generations ago the cultural empire of the Celts stretched from the Black Sea to Ireland and the Highlands of Scotland. In six hundred years, the Celts had produced some of the finest artistic and scientific masterpieces of the ancient world.