An additional classification of sources that have been employed to augment or supplement the classical narratives of the Druids comprises references to them in medieval Irish and Welsh literature, whether explicit or speculative. Since scholarly analysis of the subject began in Britain at the beginning of the eighteenth century, such references have been utilized for this purpose. In Ireland, attempts to write objective histories of the Druids and the production of literary images of them almost blend together. However, for two reasons, this Celtic vernacular literature has had a lesser influence on the British than the Graeco-Roman authors. One is that ancient Greek and Roman literature have always been taught in greater depth in British schools of thought than Celtic themes.

Another concern is that the Irish and Welsh texts have frequently been regarded as less reliable due to the fact that the surviving versions were all compiled centuries after the conversion of the respective peoples to Christianity, which is commonly believed to have entailed the abandonment of Druidry. Therefore, they function as retrospective narratives of a long-extinct civilization, in contrast to the Greek and Roman authors who were either present during the time period they chronicled or relied on written sources or recollections that were comparatively recent.

In response to this argument, proponents of Celtic literature have consistently maintained that it originated from societies where Druids had flourished, and is therefore devoid of the prejudice, hostility, and misunderstanding that are so readily apparent or assumed in classical authors.

Until recently, a presumption that dominated the study of medieval Irish literature between the mid-nineteenth and late twentieth centuries significantly bolstered the latter position. This was due to the fact that the epic tales in that body of literature were derived from pre-Christian tales that had been passed down orally through a flourishing tradition of repetition and recitation until they were recorded at various points during the early and high medieval periods. They belonged to a select group of bards whose social standing and education, similar to the narratives they narrated, had endured the advent of Christianity virtually unaltered.

An additional classification of sources that have been employed to augment or supplement the classical narratives of the Druids comprises references to them in medieval Irish and Welsh literature, whether explicit or speculative.

This hypothesis was established upon two highly credible pieces of evidence. One was that, as demonstrated, Greek and Roman authors had commented on the function of bards in Gallic society, which was precisely comparable to that which they performed among the medieval Irish and Welsh, later speakers of Celtic languages. The second was that the Irish epics were set in a pre-Christian indigenous culture that was openly admired and sympathized with, making it extremely improbable that they were written by the medieval Christians who preserved the manuscripts containing them. Moreover, given the absence of Roman conquest in Ireland, it can be hypothesized that the Druids thrived there prior to the advent of the Middle Ages, coinciding with the dissemination of literacy among their own people. This appeared to enhance the likelihood that genuine recollections of them would be preserved in written form.

Expert opinion began to shift away from these perspectives in the 1980s, as a result of the influence of the two primary scholarly instruments that could provide clarification on the subject: textual analysis and archaeology. The former drew attention to the absence of characteristics commonly associated with orally transmitted tales, which were evident in other early literary works like Homeric poems, from the medieval Irish epics. The Irish works are predominantly composed in prose, rather than verse, and are devoid of formulaic structures, key phrase repetition, alliteration, rhyme, cadence, metre, assonance, and other memorization devices. They exhibit, in fact, every indication that they were originally intended for literary purposes.

Archaeologists made the significant finding that the royal centers depicted in the stories had, in fact, been present during pagan times; however, they did not appear as the medieval authors assuredly depicted the residential halls. Conversely, they were intricate ceremonial hubs that were frequently exposed to the heavens. Subsequent authors were either cognizant of their former significance due to an enduring tradition that failed to safeguard an exact documentation of their configuration or function, or they were merely speculating on the basis of archaeological findings scattered across the terrain.

The architecture, attire, and weaponry depicted in the epics were all from the Middle Ages, not the Iron Age. Certain species of animals that were not indigenous to Ireland are described, while others were introduced subsequent to the arrival of Christianity. One could argue that authentically ancient tales were merely being retold with modern embellishments, similar to how Shakespeare enacted the unequivocally historical circumstances surrounding Julius Caesar’s demise while dressed in Elizabethan attire. In contrast, Shakespeare utilized sources that originated during the reign of Caesar and pertained to the pre-Christian era, whereas the medieval Irish authors lacked comparable materials to take inspiration from.

J. P. Mallory encapsulated a growing consensus in 1992 when he stated that “in general, it is impossible to make a convincing case for an Iron Age date for the earliest recorded Irish epics, regardless of the data manipulation strategies that are attempted.”
This raises the question of why Christian Irish writers during the Middle Ages attempted to recreate the splendors of a pagan and prehistoric era; however, this inquiry has been satisfactorily resolved. It is evident that Irish monasteries had emerged as formidable forces of Western civilization by the seventh century, surpassing the British populace in their expertise on Greek and Latin manuscripts and knowledge of these languages. In addition to the Bible and other significant early Christian writings, they possessed knowledge of some of the most renowned works from pagan Greece and Rome.

They labored assiduously over the course of the subsequent five hundred years to both produce their own great works of literature and situate themselves within the overarching framework of European history that classical authors had established. They combined concepts and images from the Bible, other Christian texts, classical Greek and Latin works, and a substantial amount of indigenous tradition in this wildly successful endeavor.

However, our understanding of the extent to which this tradition was authentic and the extent to which it was fabricated due to the absence of a superior alternative remains uncertain. Undoubtedly, the authors endeavored to persuade readers and listeners of its veracity by situating stories in deserted locales, alluding to defunct political systems, and employing verse styles that had become archaic by the time the remaining stories were crafted. Unknown is whether any of their material was derived from authentic pre-medieval oral traditions and, if so, which specific tradition it was.