The Druids combined the functions of the priest, the magistrate, the scholar, and the physician. They stood to the people of the Celtic tribes in a relation closely analogous to that in which the Brahmans of India, the Magi of Persia, and the priests of the Egyptians stood to the people respectively by whom they were revered. 

The Druids taught the existence of one god, to whom they gave a name "Be'al," which Celtic antiquaries tell us means "the life of every thing," or "the source of all beings," and which seems to have affinity with the Phoenician Baal. What renders this affinity more striking is that the Druids as well as the Phoenicians identified this, their supreme deity, with the Sun. Fire was regarded as a symbol of the divinity. The Latin writers assert that the Druids also worshipped numerous inferior gods. 

They used no images to represent the object of their worship, nor did they meet in temples or buildings of any kind for the performance of their sacred rites. A circle of stones (each stone generally of vast size) enclosing an area of from twenty feet to thirty yards in diameter, constituted their sacred place. The most celebrated of these now remaining is Stonehenge, on Salisbury Plain, England. 

These sacred circles were generally situated near some stream, or under the shadow of a grove or wide-spreading oak. In the center of the circle stood the Cromlech or altar, which was a large stone, placed in the manner of a table upon other stones set up on end. The Druids had also their high places, which were large stones or piles of stones on the summits of hills. These were called Cairns, and were used in the worship of the deity under the symbol of the sun. 

The Druids observed two festivals in each year. The former took place in the beginning of May, and was called Beltane or "Fire of God." On this occasion a large fire was kindled on some elevated spot, in honor of the sun, whose returning beneficence they thus welcomed after the gloom and desolation of winter. 

The other great festival of the Druids was called "Samh'in," or "Fire of Peace," and was held on Hallow-eve, (first of November) which still retains this designation in the Highlands of Scotland. On this occasion the Druids assembled in solemn conclave, in the most central part of the district, to discharge the judicial functions of their order. 

All questions, whether public or private, all crimes against person or property, were at this time brought before them for adjudication. With these judicial acts were combined certain rituals, especially the kindling of the sacred fire, from which all the fires in the district, which had been beforehand scrupulously extinguished, might be relighted. This usage of kindling fires on Hallow-eve lingered in the British islands long after the establishment of Christianity. 

Besides these two great annual festivals, the Druids were in the habit of observing the full moon, and especially the sixth day of the moon. On the latter they sought the Mistletoe, which grew on their favorite oaks, and to which, as well as to the oak itself, they ascribed a peculiar virtue and sacredness. The discovery of it was an occasion of rejoicing and solemn worship. 

The Druids were the teachers of morality as well as of religion. Of their ethical teaching a valuable specimen is preserved in the Triads of the Welsh Bards, and from this we may gather that their views of moral rectitude were on the whole just, and that they held and inculcated many very noble and valuable principles of conduct. They were also the men of science and learning of their age and people. 

Their teaching was oral, and their literature (if such a word may be used in such a case) was preserved solely by tradition. But the Roman writers admit that "they paid much attention to the order and laws of nature, and investigated and taught to the youth under their charge many things concerning the stars and their motions, the size of the world and the lands, and concerning the might and power of the immortal gods." 

Their history consisted in traditional tales, in which the heroic deeds of their forefathers were celebrated. These were apparently in verse, and thus constituted part of the poetry as well as the history of the Druids. In the poems of Ossian we have, if not the actual productions of Druidical times, what may be considered faithful representations of the songs of the Bards. 

The Bards were an essential part of the Druidical hierarchy. One author, Pennant, says, "The Bards were supposed to be endowed with powers equal to inspiration. They were the oral historians of all past transactions, public and private. They were also accomplished genealogists." 

The Druidical system was at its height at the time of the Roman invasion under Julius Caesar. Against the Druids, as their chief enemies, these conquerors of the world directed their unsparing fury. The Druids, harassed at all points on the main land, retreated to Anglesey and Iona, where for a season they found shelter and continued their now-dishonored rites. 

The Druids retained their predominance in Iona and over the adjacent islands and main land until they were supplanted and their way of life and religion overturned by the arrival of St. Columba, the apostle of the Highlands, by whom the inhabitants of that district were first led to profess Christianity.