He is one of the best-documented figures of the Christian church in the British Isles during the sub-Roman period, and was renowned for his Biblical knowledge and literary style.

He was educated at a monastic centre, the College of St. Illtud, where he chose to forsake his royal heritage and embrace monasticism.

He eventually founded a monastery for these students at Saint-Gildas-de-Rhuys in Brittany, where he wrote De Excidio Britanniae, criticising British rulers and exhorting them to put off their sins and embrace true Christian faith.

[8] According to this tradition, Gildas is the son of Caunus, king of Alt Clud in the Hen Ogledd, the Brythonic-speaking region of northern Britain.

He was supposed to be educated in liberal arts and divine scripture, but elected to study only holy doctrine, and to forsake his noble birth in favour of a religious life.

He returned to his native lands in northern Britain where he acted as a missionary, preaching to the pagan people and converting many of them to Christianity.

Gildas obeyed the king's summons and travelled all over the island, converting the inhabitants, building churches, and establishing monasteries.

Intending to return to Britain, he instead settled on the Isle of Houat off Brittany where he led a solitary, austere life.

[11] The Llancarfan life also contains the earliest surviving appearance of the abduction of the Guinevere episode, common in later Arthurian literature.

Gildas secures the release of Guinevere after she had been abducted by Melvas, king of the "Summer Country", preventing war between him and Arthur.

He excoriates his fellow Britons for their sins, while at the same time lauding heroes such as Ambrosius Aurelianus, whom he is the first to describe as a leader of the resistance to the Saxons.

Part two consists of a condemnation of five British kings, Constantine, Aurelius Conanus, Vortiporius, Cuneglasus, and Maelgwn.

Gildas is credited with a hymn called the Lorica, or Breastplate, a prayer for deliverance from evil, which contains specimens of Hiberno-Latin.