The earliest source to describe the Battle of Mons Badonicus is De Excidio et Conquestu Britanniae ( On the Ruin and Conquest of Britain ), written by the monk Gildas in the mid 6th century.

Excepting the 6th century jeremiad by Gildas and the poetry attributed to Taliesin and Aneirin, in particular Y Gododdin, thought to have been composed in Scotland in the 7th century, Welsh sources generally date from a much later period.

The establishment of barbarian bases inland rendered the extensive coastal forts of the Saxon Shore almost useless as the 6th Century British monk Gildas laments:

In the late 18th century attempts were made to identify Aneirin with the early 6th century writer, Gildas, based on the incorrect form of his name.

Variants of the name Dumnonia include Domnonia and Damnonia, the latter being used by Gildas in the 6th century as a pun on " damnation " to deprecate the area's contemporary ruler Constantine.

Vortiporius, " tyrant of the Demetae ", is one of the kings condemned by Gildas in his 6th century polemic De Excidio et Conquestu Britanniae.

According to legend in the 6th century Saint Gildas lived on Steep Holm visiting his friend Saint Cadoc, who lived on Flat Holm as a hermit.

Some of the earliest mentions are in the 5th century, St. Patrick calls the Irish " Scoti ", and in the 6th century, St. Isidore bishop of Seville and Gildas the British historian both refer to Ireland as Scotia.

He also appears in Gildas ' 6th century polemic De Excidio et Conquestu Britanniae and Bede's Historia Ecclesiastica gentis Anglorum.

Ambrosius Aurelianus, ; called Aurelius Ambrosius in the Historia Regum Britanniae and elsewhere, was a war leader of the Romano-British who won an important battle against the Anglo-Saxons in the 5th century, according to Gildas.

Ambrosius Aurelianus is one of the few people that Gildas identifies by name in his sermon De Excidio et Conquestu Britanniae, and the only one named from the 5th century.

Sources for events after this date are extremely scarce, but a tradition, reported as early as the mid-6th century by a British priest named Gildas, records that the British sent for help against the barbarians to Aetius, a Roman consul, probably in the late 440s.

The British thus gained a respite, and peace lasted at least until the time Gildas was writing: that is, for perhaps forty or fifty years, from around the end of the 5th century until midway through the sixth.

The peace following the battle of Mons Badonicus is attested partly by Gildas, a monk, who wrote De Excidio et Conquestu Britanniae or On the Ruin and Conquest of Britain during the middle of the sixth century.

According to the Life of Saint Gildas, written in the early 12th century by Caradoc of Llancarfan, Arthur is said to have killed Gildas ' brother Hueil and to have rescued his wife Gwenhwyfar from Glastonbury.

In the 9th century work Historia Brittonum, the victory is attributed to the battle-leader Arthur and various later texts follow this attribution, though the only near-contemporary account of Badon, written by Gildas, does not mention Arthur nor does it explicitly state the identity of the victors.

That Arthur is not mentioned in the earliest source, Gildas, was noticed as early as the 12th century.

The tonsure is also mentioned in a passage, probably of the 7th century but attributed wrongly to Gildas ; " Britones toti mundo contrarii, moribus Romanis inimici, non solum in misa sed in tonsura etiam " (" Britons are contrary to the whole world, enemies of Roman customs, not only in the Mass but also in regard to the tonsure ").

There are two Lives of Gildas: the earlier written by a monk of Rhuys in Brittany, possibly in the 9th century, the second written by Caradoc of Llancarfan, a friend and contemporary of Geoffrey of Monmouth, composed in the middle of the 12th century.

The 6th-century historian Gildas wrote De Excidio et Conquestu Britanniae () in the first decades of the sixth century.

Andrew Breeze argued that Gildas received his later education in Cirencester in the early sixth century, showing that it was still able to provide an education in Latin rhetoric and law at this time.

Just before and after the second World war, Gildas Jaffrenou built a harp from the 14th century plans for the Brian Boru model.

Life of Saint Gildas, written in the early 12th century by Caradoc of Llancarfan ; of Saint Cadoc, written around 1100 or a little before by Lifris of Llancarfan ; medieval biographies of Carannog, Padarn and Eufflam, probably written around the 12th century ; a less obviously legendary account of Arthur appears in the Legenda Sancti Goeznovii, which is often claimed to date from the early 11th century ; William of Malmesbury's De Gestis Regum Anglorum and Herman's De Miraculis Sanctae Mariae Laudensis, which together provide the first certain evidence for a belief that Arthur was not actually dead and would at some point return.

Gildas ' 6th-century polemic De Excidio et Conquestu Britanniae ( On the Ruin and Conquest of Britain ), written within living memory of Mount Badon, mentions the battle but does not mention Arthur.

In the De Excidio et Conquestu Britanniae written c. 540, Gildas says that Maximus left Britain not only with all of its Roman troops, but also with all of its armed bands, governors, and the flower of its youth, never to return.

* Gildas De Excidio et Conquestu Britanniae II. 13-14

* Gildas, De Excidio Brittaniae, ed.

Gildas ' principal work, De Excidio et Conquestu Britanniae, is a sermon in three parts condemning the acts of his contemporaries, both secular and religious.

The only contemporary information about the person is provided by Gildas, who includes Maelgwn among the five British kings who he condemns in allegorical terms in his De Excidio et Conquestu Britanniae.

In his De Excidio et Conquestu Britanniae (), written c. 540, Gildas makes an allegorical condemnation of 5 British kings by likening them to the beasts of the Christian Apocalypse as expressed in the biblical Book of Revelation, 13-2: the lion, leopard, bear, and dragon, with the dragon supreme among them .< ref >* — " And the beast which I saw was like unto a < u > leopard </ u >, and his feet were as the feet of a < u > bear </ u >, and his mouth as the mouth of a < u > lion </ u >: and the < u > dragon </ u > gave him his power, and his seat, and great authority.

In his condemnation of 5 British kings in the De Excidio et Conquestu Britanniae, Gildas refers to wine as " sodomitical " but never applies that word to any person.

Some experts say that this was not the first compiled history of the Britons and that it was largely based on Gildas ' De Excidio et Conquestu Britanniae written some two centuries before.

St Gildas, the Welsh author of the De excidio Britonum, is also credited with the Lorica, or Breastplate, an apotropaic charm against evil that is written in a curiously learned vocabulary ; this too probably relates to an education in the Irish styles of Latin.

Chroniclers such as Bede, with his Historia ecclesiastica gentis Anglorum, and Gildas, with his De Excidio et Conquestu Britanniae, were figures in the development of indigenous Latin literature, mostly ecclesiastical, in the centuries following the withdrawal of the Roman Empire.

In 1525 Vergil published an edition of Gildas ' 6th-century history, De Excidio et Conquestu Britanniae, probably at Antwerp.

He is attributed in some old stories as hosting the first Eisteddfod and he is one of five Celtic British kings castigated for their sins by the contemporary Christian writer Gildas ( who referred to him as Maglocunus, meaning ' Prince-Hound ' in Brittonic ) in De Excidio et Conquestu Britanniae.

"... you the last I write of but the first and greatest in evil, more than many in ability but also in malice, more generous in giving but also more liberal in sin, strong in war but stronger to destroy your soul ...." Gildas Sapiens, De Excidio et Conquestu Britanniae

* Britannicarum Gentium Historiæ Antiquæ Scriptores tres: Ricardus Corinensis, Gildas Badonicus, Nennius Banchorensi ( 1757 ) – his notable work, a publication of the works of Gildas, Nennius, and the purported author of De Situ Britanniæ, Richard of Cirencester.

In desperation the Britons send letters to the general of the Roman forces, asking for help, but receive no reply ( this passage borrows heavily from the corresponding section in Gildas ' De Excidio Britanniae ).

The works of Gildas Sapiens, including the Excidio, can be found in volume 69 of the Patrologia Latina.

Gildas mentions Constantine in chapters 28 and 29 of his 6th-century work De Excidio et Conquestu Britanniae.

Geoffrey of Monmouth includes Constantine in a section of his Historia Regum Britanniae adapted from Gildas, in which the reproved kings are made successors, rather than contemporaries as in De Excidio.

Gildas discusses Aurelius Conanus in Chapter 30 of his work De Excidio et Conquestu Britanniae, in a section in which he reproves five kings for their various sins.

The only contemporary information about the person comes from Gildas, in a highly allegorical condemnation from his De Excidio et Conquestu Britanniae ().