I am learning from reading and from such programs that I find on the Discovery channel that the celts were also great astronomers - on a level par with the Egyptians and Aztecs with their pyramids, althought the celts used great stones and various carvings and land formations to mark the celestial bodies rather than great monumental buildings.
I watched a program last evening "Ancient Astronauts" on Discovery Science, about a Celtic worship site - it seems that when the ceremonial drums and music were played, the entire structure resonanted in such a way as to alter brain waves - something the documentary called "Delta Wave" patterns in the human brain. These Delta patterns produced an effect of completely relaxing the body, while leaving the mind in a highly alert mental state. They stated that this was how shamans were able to produce altered states of being, to literarly speak and commune with thier gods.
RPG Anne O'Calahan