Saint Gildas (c. 494 or 516 – c. 570) was a prominent member of the Celtic Christian church in Britain, whose renowned learning and literary style earned him the designation Gildas Sapiens (Gildas the Wise). He was ordained in the Church, and in his works favored the monastic ideal. Fragments of letters he wrote reveal that he composed a Rule for monastic life that was a little less austere than the Rule written by his contemporary, Saint David, and set suitable penances for its breach.

Life
The first Life written at Rhuys by an unnamed scribe says that Gildas was the son of Caunus (Caw), born in the district of Arecluta (Alt Clut or Strathclyde). He was entrusted into the care of Saint Hildutus (Illtud) along with Samson and Paul, to be educated. He later went to Iren (Ireland) to continue his studies. Having been ordained, he went to North Britain to preach to the unconverted. Saint Brigidda (Brigit, died 524) asked for a token and Gildas made a bell which he sent to her. Ainmericus, King of all Ireland (Ainmere, 566-569), asked Gildas to restore church order, which he did. He went to Rome and then Ravenna. He came to Brittany and settled on an island (Rhuys), where he lived a solitary life. Later, he built a monastery there. He built an oratory on the bank of the River Blavetum (River Blavet). Ten years after leaving Britain, he wrote an epistolary book, in which he reproved five of the Brythonic kings. He died at Rhuys on 29 January, and his body, according to his wishes, was placed on a boat and allowed to drift. Three months later, on 11 May, men from Rhuys found the ship in a creek with the body of Gildas still intact. They took the body back to Rhuys and buried it there.

Rhuys Life
Caradog of Llancarfan, influenced by Geoffrey of Monmouth and his Norman patrons, and drawing on the Life of Cadog among other sources, paints a somewhat different picture including the statements that Gildas was educated in Gaul, retired to a hermitage dedicated to the Trinity (at Street) near Glastonbury and was buried at Glastonbury Abbey. Some scholars who have studied the texts suspect the latter to be a piece of Glastonbury propaganda.
Caradog tells a story of how Gildas intervened between King Arthur and a certain King Melwas of the 'Summer Country' who had abducted Guinevere and brought her to his stronghold at Glastonbury, where Arthur soon arrived to besiege him. However, the peacemaking saint persuaded Melwas to release Guinevere and the two kings made peace. Caradog also says that the brothers of Gildas rose up against Arthur, refusing to acknowledge him as their lord. Arthur pursued Huail ap Caw, the eldest brother, and killed him. Gildas was preaching in Armagh in Ireland, at the time, and he was grieved by the news.

Llancarfan Life
A strongly held tradition in north Wales places the beheading of Gildas' brother, Huail, at Ruthin, where what is believed to be the actual execution stone has been preserved in the town square. Another brother of Gildas, Celyn ap Caw was based at Garth Celyn on the north coast of Gwynedd together with the territory of land watching over the Copper Mountain on Anglesey.
Gildas is credited with a hymn called the Lorica, or Breastplate, a prayer to be delivered from evil, which contains interesting specimens of Hiberno-Latin. A proverb is also attributed to Gildas mab y Gaw in the 'Englynion y Clyweid' in Llanstephan MS. 27.
In Bonedd y Saint, Gildas is recorded as having three sons and a daughter. Gwynnog ap Gildas and Noethon ap Gildas are named in the earliest tracts, together with their sister Dolgar. Another son, Tydech, is named in a later document. The unreliable Iolo Morganwg adds Saint Cenydd to the list.
The scholar David Dumville suggests that Gildas was the teacher of Vennianus of Findbarr, who in turn was the teacher of St. Columba of Iona.

Further traditions
Gildas' surviving written work, De Excidio Britanniae or On the Ruin of Britain, is a sermon in three parts condemning the acts of his contemporaries, both secular and religious. The first part consists of Gildas' explanation for his work and a brief narrative of Roman Britain from its conquest under the principate to Gildas' time:
Concerning her obstinacy, subjection and rebellion, about her second subjection and harsh servitude; concerning religion, of persecution, the holy martyrs, many heresies, of tyrants, of two plundering races, concerning the defense and a further devastation, of a second vengeance and a third devastation, concerning hunger, of the letter to Agitius [usually identified with the patrician Aëtius], of victory, of crimes, of enemies suddenly announced, a memorable plague, a council, an enemy more savage than the first, the subversion of cities, concerning those whose survived, and concerning the final victory of our country that has been granted to our time by the will of God.
In the second part, opening with the assertion "Britain has kings, yet they are tyrants; it has judges, yet they are undutiful", Gildas addresses the lives and actions of five contemporary rulers: Constantine of Dumnonia, Aurelius Caninus, Vortiporius of the Demetae (now called Dyfed), Cuneglasus apparently of 'the Bear's Home' (possibly 'the Bear's Stronghold' - Dinarth at Llandrillo-yn-Rhôs near Llandudno), and lastly Maglocunus or Maelgwn. Without exception, Gildas declares each of these rulers cruel, rapacious, and living a life of sin.
The third part begins with the words, "Britain has priests, but they are fools; numerous ministers, but they are shameless; clerics, but they are wily plunderers." Gildas continues his jeremiad against the clergy of his age, but does not explicitly mention any names in this section, and so does not cast any light on the history of the Christian church in this period.
Gildas's work is of great importance to historians, because although it is not intended primarily as history, it is almost the only surviving source written by a near-contemporary of British events in the fifth and sixth centuries. The usual date that has been given for the composition of the work is some time in the 540s, but it is now regarded as quite possibly earlier, in the first quarter of the sixth century, or even before that.
The vision presented in this work of a land devastated by plundering raiders and the misrule of corrupt and venial officials has been readily accepted by scholars for centuries, because not only did it fit the accepted belief of invading, destructive barbarians who destroyed Roman civilization within the bounds of the former empire, but it also explained away the awkward question of why Britain was one of the few parts of the Roman Empire that did not acquire a Romance language, as had France and Spain. However, the student must remember that Gildas' intent in his writing is to preach to his contemporaries after the manner of an old testament prophet, not to write an account for posterity: while Gildas offers one of the first descriptions of the Hadrian's Wall -- albeit highly historically inaccurate -- he also omits details where they do not contribute to his message. Nonetheless, it remains an important work for not only Medieval but English history for being one of the few works written in Britain to survive from the sixth century.
In De Excidio Britanniae, Gildas mentions that the year of his birth was the same year that the Battle of Mons Badonicus took place in. The Annales Cambriae gives the year of his death as 570; however the Annals of Tigernach date his death to 569.
Gildas's treatise was first published in 1525 by Polydore Vergil, but with many avowed alterations and omissions. In 1568 John Josseline, secretary to Archbishop Parker, issued a new edition of it more in conformity with manuscript authority; and in 1691 a still more carefully revised edition appeared at Oxford by Thomas Gale. It was frequently reprinted on the Continent during the 16th century, and once or twice since. The next English edition, described by August Potthast as editio pessima, was that published by the English Historical Society in 1838, and edited by the Rev. J. Stevenson. The text of Gildas founded on Gale's edition collated with two other MSS, with elaborate introductions, is included in the Monumenta Historica Britannica. Another edition is in Arthur West Haddan and Will Stubbs, Councils and ecclesiastical documents relating to Great Britain and Ireland (Oxford, 1869); the latest edition is that by Theodor Mommsen in Monumenta Germaniae Historica auct. antiq. xiii. (Chronica min. iii.), 1894.

Legacy in the Anglo-Saxon Period
Gildas's work is important for reasons beyond the historical information he provides. It is clear that at the time when he was writing there was an effective (and British) Christian church. Gildas uses Latin to address his points to the rulers he excoriates; and he regards Britons, at least to some degree, as Roman citizens, despite the collapse of central imperial authority. By 597, when St Augustine arrived in Kent, what is now England was almost completely pagan, and the illiterate new rulers did not think of themselves as Roman citizens. Dating Gildas's words more exactly would hence provide a little more certainty about the timeline of the transition from post-Roman Britain to the rule of the Anglo-Saxons; a certainty that is would be the more valuable as precise dates and reliable facts are extremely scarce for this period.

Notes

Groans of the Britons
English historians in the Middle Ages