Nemetonia, original term, derived from “nemeton”
A nemeton was a sacred space of ancient Celtic religion. Nemeta appear to have been primarily situated in natural areas, and, as they often utilized trees, they are often interpreted as sacred groves. However, other evidence suggests that the word implied a wider variety of ritual spaces, such as shrines and temples. Evidence for nemeta consists chiefly of inscriptions and place-names, which occur all across the Celtic world. Toponyms related to the word nemeton occur as far west as Galicia, Spain, as far north as Scotland, and as far east as central Turkey. The word is related to the name of the Nemetes tribe living by the Rhine between the Palatinate and Lake Constance in what is now Germany, and their goddess Nemetona
Pliny and Lucan wrote that druids did not meet in stone temples or other constructions, but in sacred groves of trees. In his Pharsalia, Lucan described such a grove near Massilia in dramatic terms more designed to evoke a shiver of delicious horror among his Roman hearers than meant as proper natural history:
[N]o bird nested in the nemeton, nor did any animal lurk nearby; the leaves constantly shivered though no breeze stirred. Altars stood in its midst, and the images of the gods. Every tree was stained with sacrificial blood, the very earth groaned, dead yews revived; unconsumed trees were surrounded with flame, and huge serpents twined round the oaks. The people feared to approach the grove, and even the priest would not walk there at midday or midnight lest he should then meet its divine guardian.