W.B. Yeats, in his essay "The Celtic Element In Literature," spoke of visions of a world expressed by people who "believed that trees were divine, and could take a human or grotesque shape and dance among the shadows." Once a powerful people who dominated much of Europe, the Celts were reduced to a few small groups after the Roman invasions. However, their mythology survived, thanks largely to the efforts of medieval Irish and Welsh monks who wrote down the stories.
