For all this interest, however, we know next to nothing about Celtic religion and practices. The only sources for Celtic religious practices were written by Romans and Greeks, who considered the Celts little more than animals, and by later Celtic writers in Ireland and Wales who were writing from a Christian perspective. Simply put, although the Celts had a rich and pervasive religious culture, it has been permanently lost to human memory.
We can make some general comments about Celtic religion based on the often-hostile accounts of classical writers. The Celts were polytheistic; these gods were ultimately derived from more primitive, Indo-European sources that gave rise to the polytheistic religions of Greece, Persia, and India. The Romans in trying to explain these gods, however, linked them with Roman gods as did the Romanized Gauls so we really have no idea as to the Celtic character of these gods and their functions. We do know that Celtic gods tended to come in threes; the Celtic logic of divinity almost always centered on triads. This triadic logic no doubt had tremendous significance in the translation of Christianity into northern European cultural models.
It is almost certain that the material world of the Celts was suffused with divinity that was both advantageous and harmful. Certain areas were considered more charged with divinity than others, especially pools, lakes and small groves, which were the sites of the cental ritual activities of Celtic life. The Celts were non-urbanized and according to Roman sources, Celtic ritual involved no temples or building structures Celtic ritual life, then, was centered mainly on the natural environment.
Celtic ritual life centered on a special class, called the druides or “druids” by the Romans, presumably from a Gaulish word. Although much has been written about druids and Celtic ritual practice, we know next to nothing about either. Here’s what we can gather. As a special group, the druids performed many of the functions that we would consider “priestly” functions, including ritual and sacrifice, but they also included functions that we would place under “education” and “law.” These rituals and practices were probably kept secret a tradition common among early Indo-European peoples which helps to explain why the classical world knows nothing about them. The only thing that the classical sources attest is that the druids performed “barbaric” or “horrid” rituals at lakes and groves; there was a fair amount of consensus among the Greeks and Romans that these rituals involved human sacrifice. This may or may not be true; there is some evidence of human sacrifice among the Celts, but it does not seem to have been a prevalent practice.
According to Julius Caesar, who gives the longest account of druids, the center of Celtic belief was the passing of souls from one body to another. From an archaeological perspective, it is clear that the Celts believed in an after-life, for material goods are buried with the dead.
The earliest Celts who were major players in the classical world were the Gauls, who controlled an area extending from France to Switzerland. It was the Gauls who sacked Rome and later invaded Greece; it was also the Gauls that migrated to Asia Minor to found their own, independent culture there, that of the Galatians. Through invasion and migration, they spread into Spain and later crossed the Alps into Italy and permanently settled the area south of the Alps which the Romans then named, Cisalpine Gaul.
The Gauls were a tribal and agricultural society. They were ruled by kings, but individual kings reigned only over small areas. Occasionally a single powerful king could gain the allegiance of several kings as a kind of “over-king,” but on the whole the Gauls throughout Europe were largely an ethnic continuity rather than a single nation.
Ethnic identity among the early Gauls was very fluid. Ethnic identity was first and foremost based on small kinship groups, or clans this fundamental ethnic identity often got collapsed into a larger identity, that of tribes. The main political structures, that of kingship, organized themselves around this tribal ethnic identity. For the most part, the Gauls did not seem to have a larger ethnic identity that united the Gaulish world into a single cultural group the “Gauls” as an ethnic group was largely invented by the Romans and the Greeks and applied to all the diverse tribes spread across the face of northern Europe. The Gauls did have a sense of territorial ethnicity; the Romans and Greeks tell us that there were sixteen separate territorial nations of Gauls. These territorial groups were divided into a series of pagi, which were military units composed of men who had voluntarily united as fellow soldiers.
The Gauls, however, were not the original Europeans. Beginning in an area around Switzerland, the Celts spread westward and eastward displacing native Europeans in the process. These migrations begin around 500 BC. The Gaulish invasion of Italy in 400 was part of this larger emigration. The Romans, however, pushed them back by the third century BC; native Europeans in the north, however, were not so lucky.
Two Celtic tribes, the Cimbri and the Teutones (“Teuton,” an ethnic for Germans, is derived from the Celtic root for “people”), emigrated east and settled in territory in Germany. The center of Celtic expansion, however, was Gaul, which lay north of the Alps in the region now within the borders of France and Belgium and part of Spain.
The earliest account of the Gauls comes from Julius Caesar. In his history of his military expedition first into Gaul and then as far north as Britain, Caesar dexcribed the tribal and regional divisions among the Gauls, of which some seem to have been original European populations and not Celtic at all.
The Gaulish tribes or territories frequently built fortifications that served as the military and political center of the region. These fortified centers took their names from the larger tribe for instance, Paris took its name from the tribe of Parisi and Chartres was originally named after the tribe, the Carnuti, which had built it.