This is a true shame, for these old saints, such as David of Wales, were an integral part of the local devotional life of Catholics in the Middle Ages; for the average Welshman of the 11th century, St. David would have been a much more familiar name than St. Augustine or St. Ambrose. Medieval Catholicism, like everything else medieval, was colored by localism. Modern approaches to Catholic saints tend to focus on the lives of the "great ones" with a bird's eye view of how they changed or edified the Church Universal; for the medieval, how a saint changed or edified the Universal Church was not as interesting as the preaching and holy deeds that they did at this specific hill, that particular well or this certain bend in the road. Piety was tied to localism that was vivified by the memory of what this or that saint did at certain hallowed sites.
According to most accounts, St. David was conceived through rape, and some sources suggest that his mother was a nun (although it is also possible that this is a corruption of a proper name, "Nonna" or "Nonnita"); his father was a lord of the house of the king of Ceredigion, though the records are ambiguous as to whether the father was the king himself, the king's brother or one of the king's sons.
The various Vitae of St. David suggest that even his birth was miraculous: St. Patrick is reputed to have had a prophecy of David's birth thirty years before the fact, and at the saint's baptism (c. 500) a blind man was cured. The young David was sent to learn at the feet of of St. Illtyd (along with other Welsh saints such as Samson of Dol and Gildas) and then studied Scripture under St. Paulinus of Whitland for ten years.
The young David was sent out as a missionary priest among the British and found or restored twelve monasteries. The greatest of these was undoubtedly Glastonbury, which in the Norman era became the wealthiest monastery in the kingdom. Glastonbury is also remembered for its connections with the Holy Grail and the Arthurian legends (Arthur and Guinivere are purported to be buried there) as well as for the famous Glastonbury Thorn, a species of Hawthorne which bloomed only twice per year, once in May and once on Christmas. The original Glastonbury Thorn was cut down and burned by Cromwell's troops as a remnant of medieval superstition; another incarnation of the thorn existed until 1991. The sapphire altar of Glastonbury was one of the items plundered when Henry VIII seized the assets of the monastery during the Dissolution
His austere measures provoked anger by many monks, and like St. Benedict he was victim of some unsavory attempts at removing him. This perhaps led to his pilgrimage to Jerusalem where he received episcopal consecration by the hands of the Patriarch (possibly Peter or Macarius II). He was quickly recalled to Wales, however, to deal with the Pelagian heresy which was then raging throughout Britain. The Synod of Brevi was convened around 550; so eloquently did David preach that he was soon after appointed to the highest see in Wales, the Archbishopric of Caerleon. This Synod was also the occasion of his most famous miracle, in which the earth rose up beneath his feet as he preached, forming a small hill so as to better amplify his voice. The hill still exists today and his venerated in the village of Llanddewi Brefi, which means "Church of David on the [River] Brefi."
According to St. David's chronicler Rhygyfarch, David obtained the permission of King Arthur to remove his see from Caerleon to Menevia, from whence he governed the British Church for many years with great holiness and wisdom. He died at the great age of 147, on the day predicted by himself a week earlier. It is interesting that despite the fanciful age given at the time of David's death (147), various chronicles all agree that he lived to an extreme old age (at least 100) and all agree that he passed on Tuesday, March 1st. The traditional year of his death is 589. St. David's Day (March 1st) is a national holiday in Wales and is celebrated with parades, concerts, and water dyed red, much like water is dyed green for St. Patrick's Day in New York.