De Excidio et Conquestu Britanniae
 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. Part I is particularly notable as the earliest source to mention Aurelius Ambrosius, an important figure of British tradition credited with turning the tide against the Anglo-Saxon conquest. It also contains the earliest mention of the Britons' victory at the Battle of Mons Badonicus. The second part consists of a condemnation of five British kings, and as it is the only contemporary information about them, it is of particular interest to scholars of British history. Gildas swathes the condemnations in allegorical beasts from the Christian Apocalypse and the biblical Book of Daniel, likening the kings to the beasts described there: a lion, a leopard, a bear, and a dragon. The description is repeated in fewer words in the Book of Revelation: :And the beast which I saw was like unto a leopard, and his feet were as the feet of a bear, and his mouth as the mouth of a lion: and the dragon gave him his power, and his seat, and great authority. Revelation 13-2 (underlining added) The kings excoriated by Gildas are: * "Constantine the tyrannical whelp of the unclean lioness of Damnonia". * "thou lion's whelp Aurelius Conanus". * "Vortipore ... who like to the spotted leopard ... tyrant of the Demetians". * "Cuneglasse ... thou bear". * "dragon of the island ... maglocune". In the course of his condemnations, Gildas makes passing reference to the other beasts mentioned in the Apocalypse, such as the eagle, serpent, calf, and wolf. The ancient meaning of the allegories is a matter of debate and opinion to the present day. A dissection of the original biblical meaning of the allegories by the sometimes controversial 18th century writer Emanuel Swedenborg is given in the Explanation of his Apocalypse Revealed. A different perspective is given in James Ratton's The Apocalypse of St. John: A Commentary on the Greek Text. The reason for Gildas' disaffection for these individuals is unknown. He was selective in his choice of kings, as he had no comments concerning the kings of the other British kingdoms that were thriving at the time, such as Rheged, Gododdin, Elmet, Pengwern/Powys, or the kingdoms of modern-day southern England. That he chose only the kings associated with one king's pre-eminence (Maglocune, the "dragon") suggests a reason other than his claim of moral outrage over personal depravity. Neither outrage nor a doctrinal dispute would seem to justify beginning the condemnation of the five kings with a personal attack against Constantine's mother (the "unclean lioness"). Maelgwn (Maglocune), King of Gwynedd, receives the most sweeping condemnation and is described almost as a high king over the other kings (the power-giving dragon of the Apocalypse). The Isle of Anglesey was the base of power of the kings of Gwynedd, so describing Maelgwn as the 'dragon of the island' is appropriate. His pre-eminence over other kings is confirmed indirectly in other sources. For example, Maelgwn was a generous contributor to the cause of Christianity throughout Wales, implying a responsibility beyond the boundaries of his own kingdom. He made donations to support Saint Brynach in Dyfed, Saint Cadoc in Gwynllwg, Saint Cybi in Anglesey, Saint Padarn in Ceredigion, and Saint Tydecho in Powys. He is also associated with the foundation of Bangor. Constantine is obscure. His Damnonia is generally identified with Dumnonia, a kingdom in southwestern Britain. A number of later works refer to a king of this name in the area, but there is no contemporary evidence. Additionally, Damnonia may refer to the territory of the Damnonii, a tribe described by Ptolemy as living in what is now southwestern Scotland. The Damnonii were the predecessors to the later kingdom of Alt Clut, which was known to have had a longstanding relationship with Gwynedd and its kings, something not true of Dumnonia. Cuneglasse is the Cynglas (modern Welsh: Cynlas) of the royal genealogies, the son of Owain Whitetooth son of Einion son of Cunedda. He is associated with the southern Gwynedd region of Penllyn, and he was the ancestor of a later King of Gwynedd, Caradog ap Meirion. One of his brothers was Saint Seiriol. Aurelius Conanus, or Aurelius Caninus, cannot be connected to any particular region of Britain. John Edward Lloyd suggests a connection between this king and the degenerate descendants of the great hero Aurelius Ambrosius mentioned previously by Gildas; if this is true his kingdom may have been located somewhere in territory subsequently taken by the Anglo-Saxons. If the form Caninus should be connected with the Cuna(g)nus found in 6th-century writings, the result in the later royal genealogies would be Cynan, a commonly occurring name. However, this is a speculation. Vortiporius (Vortipore, Old Welsh Guortepir) was a king of Demetia (Dyfed) who is well-attested in both Welsh and Irish genealogies, the son of Aircol. Though it is not easily supportable on linguistic grounds, some scholars maintain that he is mentioned on a memorial stone (discovered in 1895) bearing an inscriptions in both Latin and ogham. The Latin inscription reads Memoria Voteporigis protictoris. The ogham inscription consists of a Primitive Irish spelling of the name: Votecorigas. If the man mentioned in both inscriptions was the same as Gildas' Vortiporius, we would expect the Latin and Irish forms to have been spelled *Vorteporigis and *Vortecorigas, respectively; the difference in spelling has led some to suggest that they are not the same person, though it is possible that they were related. 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.