The World Tree
In the Celtic world, the tree was the original denizen of the natural world. Trees provided everything needed to sustain life — fruit and acorns for eating, wood for shelter and weapons, fuel for warmth and cooking, and bark for medicines and tanning of leather. Without trees, life would have been very difficult, if not impossible.
Trees were not viewed as only being good for utilitarian purposes or even simply as sacred. The trees were literally gods, the venerated ancient ancestors of mankind. Each tree had its own sacred purpose. Some provided wood for making strong, flexible weapons; some provided life-saving medicines and healing salves. Many were shelter to sacred animals or birds, and some were regarded literally as doors to the Otherworld.
Communities had their own sacred trees, called bile, which usually stood on a plain or in the center of a clearing, where they represented the axis mundi, or center of the earth. The tree chosen as the bile was usually older and well established, and was preferably located near a well or stream. Assemblies would be held under this tree, and harming or cutting it was restricted under the strictest of taboos. The sacred tree represented the soul of the tuath, and its harm or destruction could mean fires, illness, or other disasters.
Druid worship took place in forest sanctuaries and around sacred lakes and pools. There can be no doubt that trees were especially important in the Celtic religion, and they were a central feature in druid worship. The druids' sanctuary was called the nemeton, or grove, wherein rituals and sacrifices would be performed. The Greek chronicler Strabo describes the assembly-place of the druids in Galatia as Drunemeton, the sacred oak grove.
The word nemeton, meaning “sacred or holy grove,” was the generic name given to the forest sanctuaries of the druids. The root neme is connected with many ancient European place names. Some connect the name of Nemed, a Celtic ancestral deity, to the naming of the sacred groves.