Merlin is probably the most enigmatic figure of the Arthurian cycle. According to Welsh lore, whenever Britain is in danger the mysterious magician and prophet will rise from his sleep in the deepest forest and come to its rescue.

Before the Romans, the Celts were the most powerful people in western and central Europe. Unlike the Romans, however, they left us very few inscriptions or other written records, so we are very incompletely informed about Celtic religion and mythology. We do know that their mythology was very complex and extensive, since many Roman writers, beginning with Caesar, have given us insight into it. The second source of data on Celtic religion is archaeology. Numerous monuments, statues, and other remains have been found and studied in Portugal, Spain, France, Belgium, the Netherlands, Germany, Switzerland, Austria, and Bohemia.

We know that in pre-Roman times there was close contact between the Celtic peoples on both sides of the Channel. Indeed, it was this contact that motivated Caesar to cross to Britain in order to punish the Belgae living there for their help to the Belgae in Belgium, whom he was fighting.