In Welsh society before the conquest–in all Celtic societies in fact–the bard/poet played a very important role in the life of society.

“The three principal endeavors of a Bard:
One is to learn and collect sciences.
The second is to teach.
And the third is to make peace
And to put an end to all injury;
For to do contrary to these things
Is not usual or becoming to a Bard.”

~THE TRIADS OF BRITAIN

http://www.joellessacredgrove.com/Celtic/history.html

“In the Celtic cultures, the Bard/Filidh/Ollave was inviolate. He could travel anywhere, say anything, and perform when and where he pleased. The reason for this was, of course, that he was the bearer of news and the carrier of messages, and, if he was harmed, then nobody found out what was happening over the next hill. In addition, he carried the Custom of the country as memorized verses…he could be consulted in cases of Customary (Common) Law. He was, therefore, quite a valuble repository of cultural information, news, and entertainment.”  http://www.pbm.com/~lindahl/articles/onbards.html

“The Celtic oral tradition, as it is generally referred to, was forbidden to be written down. To our modern outlook, this is an incredible impediment to preservation; however, the traditional myths, tales, and lyric poetry were well-preserved by a class of people called Druids, specifically a sub-group, the Bards or Poets. This elite group of people “were priests and teachers as well as entertainers” (Bellingham 11), and and it is thanks to their skills that examples of their lyric poetry survive today. The station of the Bard was an important one, and took many years of education:

. . . when he received the degree of Ollambh he also received the right to wear the mantle of crimson bird feathers, the right to carry the golden musical branch or wand of office, and to fill the highest post in the kingdom next to the king. (Hoagland xxxi)

Whether Fili or Ollambh, the Bard was “… in fact, a professor of literature and a man of letters, highly trained in the use of a polished literary medium”. (CELT) (I have used ‘fili’ throughout this paper in the interests of continuity, as there are different spellings of the word depending on which dialect of Gaelic is used.) They were members of the aristocratic caste, and as such, the Bards and Poets in ancient Gaelic Ireland were powerful; even as late as 1596, writer Edmund Spenser said these poets were “held in so high regard and estimation … that none may displease them, for feare to runne into reproach through their offense, and be made infamous in the mouths of all men” (Hoagland xxx).”  http://www.celticcafe.com/celticcafe/Books/Papers/HeatherIngemar/01_HeatherIngemar.html

In Wales, upon the advent of Christianity, the role of the bard was modified in the sense that he became more court poet, less seer.  At the same time, the great poets were remembered and revered.  (In  my book, The Good Knight, two of the characters are the most renowned bards of the twelfth century:  Hywel ap Owain Gywnedd and Gwalchmai ap Meilyr.)  The most famous Welsh bard of all time is Taliesin with his ties to Arthur, and perhaps the wizard Myrddin himself.

All of the books that we have in the Welsh language and tradition are poetry which was sung by bards:

http://bestoflegends.org/kingarthur/bards.html

http://www.maryjones.us/ctexts/index_welsh.html

Even today, Wales has a National Eisteddfod, a Celtic tradition honoring the bard, begun initially in 1176 by Lord Rhys, ruler of Dehuebarth (and much of Wales, after the death of Owain Gwynedd):  http://iantopf.hubpages.com/hub/The-Welsh-National-Eisteddfod