The sacred grove, in the imagination of the classical world, was the most characteristic and most venerated of all the sanctuaries of the Celtic peoples, a place where the Druids cut the mistletoe, performed their sacrifices, and gathered for the deliberations of their order. To explore the sacred groves of the ancient Celts is to enter the heart of the older Celtic religion, mythology, and spirituality, and to follow one of the most important and most fully documented of all the sacred sites and pilgrimage traditions of the Celtic world. The grove was, by general agreement of the classical and medieval sources, a place where the boundary between the human and the divine was thinnest, and the survival of the older cult of the trees, in transformed form, into the present is a striking example of the enduring power of the older Celtic sacred geography.
The Classical Sources
The principal classical source for the sacred groves of the ancient Celts is the account of Julius Caesar in his Commentarii de Bello Gallico, written in the 50s BCE. Caesar, who had ample opportunity to observe the religious practices of the Gauls, reports that the Druids of Gaul had one central sanctuary that was held in special veneration, located in the territory of the Carnutes, a powerful Gallic tribe whose territory lay in what is now the region around Chartres in central France. According to Caesar, the sanctuary was a sacred grove, and the Druids of all Gaul met there annually to settle disputes and to conduct the business of the order. The penalty for cutting the trees of the grove was death, and the grove was held in such reverence that the local population, who lived in the territory of the Carnutes, enjoyed a special protection because of the presence of the sanctuary.
The other classical sources, while they add details, also confirm the importance of the sacred grove. Strabo, writing in the late first century BCE, mentions several sacred groves in Gaul where the Druids performed their rites, and he notes that the trees of the groves were carefully preserved. Pomponius Mela, writing in the first century CE, describes the groves as the dwelling places of the gods, and he notes that the Celtic peoples believed that the presence of the divine was particularly strong in the groves. Lucan, in his epic poem Pharsalia, written in the first century CE, mentions a sacred grove near Massilia (modern Marseille) that was famous for its ancient oaks and its Druidic ceremonies, and his description of the grove, with its cold, dark interior, its inhabitants who feared the daylight, and its ancient trees that had never been cut, is one of the most vivid classical accounts of a Celtic sacred site.
The Cutting of the Mistletoe
The most famous single ritual associated with the Celtic sacred grove is the cutting of the mistletoe, as described by Pliny the Elder in his Naturalis Historia. According to Pliny, the Druids of Gaul considered nothing more sacred than the mistletoe and the oak on which it grew, and they performed a ritual at a particular phase of the moon, the sixth day after the new moon, in which the mistletoe was cut from the oak with a golden sickle. A Druid, dressed in white robes, climbed the oak and cut the mistletoe, while two white bulls, brought for the occasion, were sacrificed at the foot of the tree. The mistletoe, which was caught in a white cloth before it could touch the ground, was then distributed among the people, who believed that it had the power to ensure fertility and to protect against poison.
The account of Pliny famous descriptions of a Celtic ritual to survive, and it has become an iconic image in the popular imagination of the older Celtic religion. The mistletoe, which was the rare and revered mistletoe of the oak (Viscum album) rather than the more common mistletoe of the apple or the poplar, was a particular focus of ritual, and the ceremony of cutting it was probably one of the major annual rites of the Druidic calendar. The fact that the cutting was done with a golden sickle, the fact that the mistletoe was caught in a white cloth before it could touch the ground, and the fact that the ceremony was performed at a particular phase of the moon all attest to the care with which the ritual was performed and to the importance attached to it.
The Nemeton
The word nemeton, in the continental Celtic languages, was the term for a sacred grove or a sacred clearing, and the word is preserved in a number of place names and personal names from across the Celtic-speaking world. The Nemausus, the god of the spring at Nîmes, whose name is preserved in the name of the city, is probably a personification of the nemeton itself. The Augustonemetum of the Arverni, the modern Clermont-Ferrand, is another place name that contains the element, as does the Vernemetum of the Aedui, the modern Malain, a sanctuary in central Gaul that was famous for its sacred grove. The personal names that contain the element, including Nemetius and Nemetia, are similarly widespread, and they attest to the importance of the nemeton in the religious vocabulary of the continental Celts.
The nemed in the Irish tradition is the direct descendant of the continental nemeton, and the word was used to refer to a sacred enclosure, a sanctuary, or a place of worship. The nemed of the goddess Brigid at Cill Dara (Kildare) in Ireland, the nemed of Tlachtga in County Meath, and the nemed of the various other deities in the medieval Irish sources are all examples of the older tradition. The nemed was typically a circular or oval enclosure, often defined by a bank or a wall, within which the sacred objects and the dwelling of the deity were located. The medieval Irish nemed was often associated with a sacred tree, a sacred well, or a sacred fire, and the combination of these elements was a distinctive feature of the older Irish sacred sites.
The Archaeological Evidence
The archaeological evidence for the Celtic sacred groves is sparser than the literary evidence, since the groves themselves, being made of wood, have not survived. The places where the groves once stood can sometimes be identified by the pattern of votive deposits that have been found in and around them, and a number of sites in continental Europe and the British Isles have been interpreted as the locations of ancient sacred groves. The Heidenpütz in the Eifel region of Germany, a sanctuary that continued to attract votive deposits well into the Roman period, has been identified as a possible site of a sacred grove, and the Silva Carbonaria, the charcoal forest on the border between Roman Gaul and Germania, was a sacred forest that gave its name to a Roman provincial boundary.
The Furfooz sanctuary in Belgium, with its circular arrangement of votive deposits and its associated spring, has been interpreted as a sacred grove. The Gournay-sur-Aronde sanctuary in northern France, with its regular plan, its surrounding ditches, and its central enclosure, has been interpreted as a sacred precinct of the continental Celtic tradition. The Hayling Island temple in Hampshire, with its circular wooden structure and its associated votive deposits, has been interpreted as a sacred enclosure of the late Iron Age British Celtic tradition. The evidence is fragmentary, but it confirms the broad picture given by the literary sources: the sacred grove was a real feature of the Celtic landscape, and the ritual practices associated with it were a real feature of the older Celtic religion.
The Roman Suppression
The Roman conquest of Gaul in the late first century BCE brought the sacred groves under direct Roman pressure. Tiberius, the Roman emperor from 14 to 37 CE, issued an edict suppressing the Druidic order, partly because of the perceived threat of Druidic political influence and partly because of the Roman distaste for practices such as human sacrifice. Claudius, the emperor from 41 to 54 CE, reinforced the prohibition, and by the second century CE the formal Druidic order had largely disappeared from Gaul. The suppression of the sacred groves, where the Druids had performed their rites, was an important part of this process, and many of the groves were cut down or built over with Roman temples.
The persistence of the older tradition, in transformed form, is attested by a number of historical and archaeological sources. The Gallo-Roman practice of interpretatio Romana, in which the older Celtic deities were identified with their Roman counterparts, often led to the construction of Roman temples on the sites of the older sacred groves, and the older cult was preserved in the new Roman form. The great Roman-era healing sanctuaries at the sources of the Seine, the Marne, the Moselle, and many other rivers were often built on the sites of the older Celtic sacred sites, and the persistence of the older cult at these sites distinctive features of Gallo-Roman religion. The interpretatio Christiana of the Christian period, in which the older sacred sites were rededicated to Christian saints, was a further development of the same pattern, and many of the medieval Christian sanctuaries of the Celtic-speaking regions were built on the sites of the older sacred groves.
The Survival in the Insular Celtic World
In the insular Celtic world, where the Roman conquest was incomplete, the sacred grove survived in a number of forms. The Bile or sacred tree of the Irish tradition, the great ash or oak that stood at the center of an important territory, was a direct descendant of the continental nemeton. The Crann Bethadh or sacred tree of the medieval Irish sources, often identified with the Bile, was venerated as a source of life and a symbol of the continuity of the community. The sacred tree of the Welsh tradition, the Coelbren or the Craith or the Celyn (the holly), was similarly venerated, and the Crann Aird or high tree of the medieval Welsh sources, often associated with a particular territory, was a feature of the older Welsh sacred geography.
The survival of the older tradition is also attested by the Lia Fáil or Stone of Destiny at Tara, which, although it is a stone, is associated with a sacred tree in the medieval Irish sources, and by the various sacred trees of the Irish, Welsh, and Scottish traditions. The Holly Tree of the medieval Irish sources, the Broom and the Rowan of the Scottish Highland tradition, and the Yew of the Welsh churchyards are all examples of the persistence of the older cult of the trees. The Tree of Crúachain, the Tree of Uisnech, and the Tree of Rathcroghan in Ireland, and the various sacred trees of the Welsh and Scottish traditions, are all part of the same older pattern. The survival of the older tradition into the present, in the form of the maypole, the clootie tree, the rag tree, and the various other modern survivals of the older cult of the trees, is a striking example of the persistence of the older Celtic sacred geography.
The Memory of the Sacred Grove
The sacred grove, in the modern imagination, has remained one of the most evocative and most powerful images of the older Celtic religion. The image of the dark, ancient grove, with its sacred oaks, its Druids in white robes, its mysterious rituals, and its overwhelming sense of divine presence, has been a powerful source of inspiration for poets, artists, and musicians from the eighteenth century to the present. The historical reality, of course, was more complex than the popular image suggests, and the sacred grove, like the rest of the older Celtic religious tradition, was a real and important feature of the older Celtic world, with its own rituals, its own priests, and its own place in the religious and political life of the Celtic peoples.
The memory of the sacred grove, today, is preserved not only in the popular imagination but also in the surviving folk traditions of the Celtic-speaking regions. The Halloween bonfires, the Beltane bonfires, the May Day trees and maypoles, the clootie trees of the Scottish Highlands, the rag trees of Ireland and Wales, the wish trees of various parts of the Celtic-speaking world, and the various other modern survivals of the older cult of the trees are all descendants of the older tradition. The persistence of the older tradition, in some form, for more than two thousand years is itself one of the clearest examples of the lasting power of the sacred grove as a focus of the older Celtic religious imagination.