Source 2: http://www.druidsgrove.com

The main sources we have on what they did are Roman historians, such data as archeological remains can provide, and mythological literature recorded by monks in the eighth through twelfth century. Also, analogies can be drawn between the Celts and such Indo-European cultures that existed around the same time and had the same level of cultural achievement, such as the Hindu people.

Archaeology is an excellent resource for the study of Celtic history. Scientists have uncovered the remains of votive offerings to the Gods in lake bottoms, bogs, and "votive pits" (a narrow hole dug deep in the ground in which votive offerings are buried), which tell us about Celtic religion. There are also the remains of Celtic fortresses, habitations, temples, jewelry and tools. These remains speak to us not of events and people in Celtic history, but what life was like, what their technological capability was, what food they ate, what crafts and trades they practiced, what products they made and traded (which in turn tells us about their economy), and where they traveled and how they got there. These facts about Celtic social life are an important element for understanding Druidism, because it is necessary to understand the whole culture in which Druidism was situated.

The Roman historians are another important source, though they wrote on the Celts from their own points of view; Julius Caesar, for example, was in the process of conquering Gaul (what is now France; a variant of Gaelic is still spoken in Brittany) and therefore would have written a highly prejudiced account. Posidonius was trying to fit the Druids into his own Stoic philosophy. There is also an attempt to cast the old Celts in the role of the innocent and wise noble savage, uncorrupted by civilization and close to nature, as in the case of the writer Tacitus. Romans are usually under stood as "hostile witnesses", but they are the only eyewitnesses that we have.

Nevertheless they were often impressed by the Druids' grasp of mathematical and astronomical skill. One Roman author, Diogenes, placed the Druids on a list of the ancient world's wisest philosophers; a list which included the Magi of Persia, the Chaldeans (the priesthood of the Babylonians) and the Gymnosophists (an Hindu sect which preceded the Yogis), all of whom were selected for their skill in mathematics, physics, logic, and philosophy.

The best sources are the mythologies. There we can read of what the Druids did, how they behaved, what some of them said, and though the medieval manuscripts that preserved them were written and edited by Christian monks, much wisdom yet remains there. In Ireland the four chief myth cycles are the Ulster Cycle, the Fionn Cycle, the Invasion Races, and the Cycle of Kings. In Wales, the primary myths are contained in a book called The Mabinogion. In this century, a number of folklore collections were made of remaining oral-tradition stories and prayers. The famous "Carmina Gadelica", a collection of folk prayers from the Hebrides of Scotland, is an example of the use of folk tradition as a source for the study of Celtic mysticism. Two novels, "Gods and Fighting Men" and "Cuchullain of Muirthemney", produced close to the turn of the century, written by Lady Augusta Gregory, are excellent source texts for the study of Celtic spirituality, as they integrate the medieval texts with the folklore of the time.

One of the problems with studying Druidism academically is that the Druids were the subject of a number of persecutions and conquests, not only by the Romans, but also by Norsemen, Normans, Saxons, and Christians. Much Druidic wisdom was censored, evolved into something unrecognizable, or just plain lost; although it is true that the Romans never invaded Ireland, so that country became a haven for Druidic learning for a while. A modern person seeking the Druid's path must attempt to reconstruct the wisdom based on some or all of the sources discussed above. Yet in doing so, one discovers that despite the enormous amount of cultural data presumed lost, the truly Celtic disposition of the sources remains strong and clear. Much Druidic magic also can be found in the writings of contemporary Irish and Scottish artists. The Irish Literary Revival, with such authors as William Butler Yeats, Lady Augusta Gregory, and James Joyce, represent some of the expressions of Celtic spirit.

Here is what some of the Roman historians had to say about the Druids…

Diodorus:	[The Druids are] philosophers and theologians… skilled in the divine nature.
Lucan:	[addressing the Druids] To you alone is given knowledge of the Gods and heavenly powers – either this, or you only have not this knowledge….. But you assure us, no ghosts seek the silent kingdom of Erebus, nor the pallid depths of Dis' realm, but with a new body the spirit reigns in another world — if we understand your hymns [i.e. poems] death's halfway through a long life.
Ammianus:	[Druids investigate] problems of things secret and sublime.
Cicero:	[speaking about Diviciacus] [he] claimed to have that knowledge of nature that the Greeks call "physiologia" [natural science].
Julius Caesar:	[they have] much knowledge of the stars and their motion, of the size of the world and of the earth, of natural philosophy [physics].
Hippolytus:	They can foretell certain events by the Pythagorean reckoning and calculations.
Diogenes Laertius:	[attributes to Druids] …riddles and dark sayings; teachings that the gods must be worshipped, and no evil done, and manly behavior maintained.
Strabo	notes not only their practical knowledge of natural phenomenon, but also their pursuit of "moral philosophy". He also writes that the Druids teach that "men's souls and the universe are indestructible, though at time fire and water may prevail."
Mela:	Souls are eternal and there is another life in the infernal regions.

(These can be found in The Druids by Stuart Piggot, pg.113)