Historia Brittonum

The "single most important source used by Geoffrey of Monmouth in his pseudohistorical Historia Regum Britanniae"[1] and through the enormous popularity of the latter work, this version of the early history of Britain, including the Trojan origin tradition, was incorporated into subsequent chronicles of the long-running history of the land, such as the Middle English Brut of England, also known as The Chronicles of England.

Historians have conservatively assigned 828 to the earliest date for the work, which is consistent with the statement in chapter 4 that "from the Passion of Christ 796 years have passed.

[3][4][5][c] The text makes use of two narrative techniques that are generally considered not reliable by modern academic standards: synthesizing and synchronizing history.

Various specious causal connections and attempts to synchronize material from different sources and traditions also contribute to undermining the reliability of the chronicle.

[9] Re-analysing the eleven manuscript variants of Mommsen, he produced a two-stemma analysis of their hypothetical descent, noting however that “Only one branch, viz.

Dumville called the Nennian preface (Prefatio Nennii) a late forgery,[a][b] and believes that the work underwent several anonymous revisions before reaching the forms that now survive in the various families of manuscripts.

[15] Peter Field in particular has argued for the authenticity of the preface, suggesting that it was left out of many recensions because it was seen as derogatory to British scholarship.

The Historia contains a story of the king Vortigern, who allowed the Saxons to settle in the island of Britain in return for the hand of Hengist's daughter.

Vortigern found such a youth in Ambrosius, who rebuked the wise men and revealed that the disturbance was caused by two dragons buried underground.

[22] The tower story is repeated and embellished by Geoffrey of Monmouth in his Historia Regum Britanniae, though he attributes it to Merlin, saying "Ambrosius" is the sage's alternative name.

Chapter 56 discusses twelve battles fought and won by Arthur, here called dux bellorum (war leader) rather than king: At that time, the Saxons grew strong by virtue of their large number and increased in power in Britain.

The eighth battle was at the fortress of Guinnion, in which Arthur carried the image of Holy Mary ever virgin on his shoulders; and the pagans were put to flight on that day.

Some scholars have proposed that the author incorporated the list from a now-lost Old Welsh poem, based on the fact that some of the names appear to rhyme,[24] The odd description of Arthur bearing the image of the Virgin Mary on his shoulders at Guinnion might stem from a conflation of the Welsh word iscuit (shield) with iscuid (shoulders).

[28] Other scholars, however, such as Thomas Jones and N. J. Higham, argue that the Annales account is based directly on the Historia, suggesting the name of the battle was switched from the unknown Guinnion to the famous Badon, and that the icon Arthur carries was replaced with a more common one.

[32][33][34] Arthur's main protagonist in the fight is Bedwyr, later known as Sir Bedivere, and the poem also mentions the euhemerized god Manawydan.

[35] Cat Coit Celidon is probably a reference to the Caledonian Forest (Coed Celyddon) which once covered the Southern Uplands of Scotland.

[39] Attached to the Historia is a section called De mirabilibus Britanniae (or simply Mirabilia for short, a Latin word meaning 'marvels, miracles').

The first concerns Arthur's dog, Cabal (Cavall in Welsh) and the footprint it left while chasing the boar Troynt (→Troit) Twrch Trwyth: There is another marvel in the region which is called Buelt.

[46][e] The second concerns Arthur's son Anir or Amr (Amhar in Welsh) and his sepulchre: There is another wonder in the region which is called Ercing.

The document includes a collection of traditions about Saint Patrick, as well as a section describing events in the North of England in the sixth and seventh centuries, starting with a paragraph about the beginnings of Welsh literature[47] At that time, Talhaiarn Cataguen was famed for poetry, and Neirin, and Taliesin and Bluchbard, and Cian, who is called Guenith Guaut, were all famous at the same time in British poetry.