Margaret Murray was an early twentieth century scholar who popularized the idea of a pan-European, Pre-Christian pagan religion. The validity of that idea remains in question.
Her two most influential books can be found below:
A sceptical view of her theories, including examples of her selective quoting of texts to support her thesis, can be found in Norman Cohn's book, Europe's Inner Demons; ISBN: 0226113078
See Wicca, Neo-paganism, religion