One of the best books ever written on pagan gods and goddesses as they were understood during the Renaissance, this is a work Treadwell's recommends regularly. The gods were known long after Christianisation, from the medieval and later centuries across Europe -- but they were planetary powers, as moral allegories, mythic characters and spiritual ideals. Art and written works - both lyrical and prose -- made them integral parts of the lives of Europeans century after century. It was this strata of survival which allowed the pagan religious revival of the 20th century, including Wicca and druidry. Seznec is a wonderful writer, and the book is a joy to read. Illustrations through the text. 

Princeton: Princeton University Press, 1953 / 1972. Paperback, 376 pages. 

Survival of the Pagan Gods - Jean Seznec