[[caption-width-right:275:Vortigern discovers the dragons under Dinas Emrys (14th century illustration).]]

->''"The cloth represents your kingdom, and the two worms are two dragons. The red worm is your dragon, and the lake represents the world. But the white one is the dragon of the people who have seized many peoples and countries in Britain, and will reach almost from sea to sea; but later our people will arise, and will valiantly throw the English people across the sea."''
-->--'''Ambrosius''' to Vortigern, ch. 42

''Historia Brittonum'' ("History of the Britons") is a short Latin-language UsefulNotes/{{W|ales}}elsh chronicle. It was compiled around 830 from several older texts of different provenance, loosely connected by an unknown editor. The preface, which is included in most but not all manuscripts, claims that this editor was Nennius, a 9th century Welsh monk. However, modern researchers regard the preface as a forgery of later centuries to lend greater credibility to the work.

Despite its self-designation as a chronicle, the book is pseudohistory rather than history and clearly serves up [[Myth/CelticMythology ample helpings of legend]]. Nevertheless, as one of the very few sources on the era in British history otherwise known as the [[DarkAgeEurope Dark Ages]], it developed a huge impact over time; specifically, it is the first known work that offers a coherent description of [[Myth/KingArthur "King" Arthur]]'s career, and thus can be considered the first work of what would later become the “Matter of Britain”, a.k.a. the Arthurian Universe.

The book’s main theme is the struggle of Celtic Britons and UsefulNotes/AngloSaxons for control of Britain, and it does its best to paint the Anglo-Saxons as [[AlwaysChaoticEvil treacherous cutthroat barbarian riff-raff]], while extolling the ancient and glorious history of the Britons. The book’s most extravagant claim - which serves to underpin the superior pedigree of the Britons - is that they are descendants of [[UsefulNotes/TheTrojanWar refugees from Troy]], who were led to Britain by one Brutus, a descendant of [[Literature/TheAeneid Aeneas]] ([[ContinuitySnarl or is he?]]), and from whom the island of Britain received its name.

According to ''Historia Brittonum'', the culprit for the downfall of the Britons was a certain King Vortigern, who grabbed the hegemonial power over the island after [[UsefulNotes/TheRomanEmpire the Romans]] had left. When some exiled Saxons under their leaders Hengist and Horsa asked for asylum in Britain, Vortigern allowed them to settle on the island of Thanet in exchange for their military services against Picts and Irish. But once Hengist successfully sets up Vortigern with his own beautiful daughter, the autocratic king grows more and more dependent on his foreign hirelings. Eventually, Vortigern can no longer satisfy the newcomers' greed, and the scheming king of the Saxons shows his true face when, [[NastyParty after inviting them to a banquet]], he has three-hundred British nobles massacred, with Vortigern taken prisoner. Vortigern ransoms himself by ceding Essex, Sussex and Middlesex, having already given away Kent earlier.

Fed up with the Saxons and Vortigern alike, the disgruntled Britons rise under Vortigern's more virtuous son Vortimer to make war on the Saxons, while that holy man of God, Saint Germanus, flits around Britain doing miracles and reproaching the king for his plentiful vices. Eventually Vortigern, having lost all respect from his former subjects, dies two miserable deaths - the book can’t decide which one – and his rival, the noble Ambrosius takes the helm of the Britons, eventually halting the Saxon advance with the help of the Britons' greatest war-hero, the glorious [[KingArthur Arthur]]. The short account of Arthur's heroics contains most of the hard facts that constitute "{{canon}}" within traditional Welsh Arthurian lore. Most obviously, Arthur here is not called a king himself, but a "warchief" (''dux bellorum'', literally "leader of battles") and a warrior (''miles'')[[note]]though it's been argued that the text does not preclude Arthur from having been a king himself, additional text in a variant manuscript makes his less-noble status more explicit, showing there was indeed at least a tradition about a non-royal Arthur.[[/note]]

On a minor note, the book also veers into Myth/{{Irish mythology}} by recounting the legendary traditions about the settlement and early history of UsefulNotes/{{Ireland}}, and dedicates a section to St. Patrick. The final part, strangely enough (obviously just another loosely related appendix tacked on at the end) are genealogies of Anglo-Saxon kings, all of whom are traced back to the god Woden.

While the book was (unsurprisingly) little read outside of Wales, it was, 300 years later, the most important text source for Geoffrey of Monmouth’s ''Literature/HistoriaRegumBritanniae'', who repeated the key points of ''Historia Brittonum'' but expanded greatly on its framework.

''Historia Brittonum'' at [[http://www.gutenberg.org/ebooks/1972 Project Gutenberg]] and [[http://en.wikisource.org/wiki/History_of_the_Britons Wikisource]].
!! ''Historia Brittonum'' provides examples of the following tropes:

* BoltOfDivineRetribution: According to death Nr. 1, Vortigern, having refused to better his sinful ways despite the exhortations of St. Germanus, was killed when "fire fell suddenly from heaven" and burned him with his entire castle. Even before Vortigern, the very same thing happened to the pagan king Benlli, who had refused to admit Germanus to his city. You don't snub this saint, or else!
* ChronicBackstabbingDisorder: Having already betrayed and murdered three Roman governors, the Britons feel they can't hold their ground against the Scots (= Irish) and Picts, so they send an embassy to Rome to ruefully implore the Romans to send another governor. The Romans send an army that drives off the invaders and installs a new governor. Cue the Britons feeling oppressed and [[UngratefulBastard massacring the Roman administration]]. And then ... then they send another rueful embassy to Rome to [[EntitledBastard plead for military aid]].
* ContinuitySnarl: Big time -- a testament to the book being glued together from various texts that don't harmonize all that well with each other.
** The book can’t decide whether Brutus, the first King of Britain, is the grandson or the great-great-great-grandson of Aeneas, whether he is identical to Brutus the first consul of Rome, or whether maybe he was descended from Japheth, the son of Noah, and not related to Aeneas at all.
** The number of the Emperors that visited Britain is variously given as seven or nine.
** The book acknowledges that there are two quite different stories about Vortigern's death, and just tells them both.
* DeathByChildbirth: Brutus' mother dies at his birth.
* EarlyInstallmentWeirdness: For Arthurian lore. Arthur isn't a king, Ambrosius is considered the most glorious king of the Britons instead, and there's no Myth/{{Merlin}}, no Guinever, no Table Round, no Grail, no Excalibur, and no Knights. There's basically nothing of what defines Arthur in the writings of Creator/ChretienDeTroyes and Creator/ThomasMalory.
* FolkHero: Judging from ''Historia Brittonum'', Arthur may have been this type of hero in his beginnings -- a war-hero of comparatively low birth who kicked Saxon butt and saved the British kings' asses. As none of the surviving manuscripts of the work are identical, an edition known as the "Vatican recension" also includes the following line which makes Arthur's lower birth more explicit:
-->''"And though there were ''many more noble than himself'', yet he was twelve times chosen their commander, and was as often conqueror."''
%%* TheGoodKing: Ambrosius. %% Zero Context
* HowTheMightyHaveFallen: Vortigern's death No. 2 has him reduced to a deserted refuge wandering around Britain:
-->''Others assure us, that being hated by all the people of Britain, for having received the Saxons, and being publicly charged by St. Germanus and the clergy in the sight of God, he betook himself to flight; and, that deserted and a wanderer, he sought a place of refuge, till broken hearted, he made an ignominious end.''
* NastyParty: Hengest invites King Vortigern with three hundred British nobles to talk peace and party, but when they are sitting at table the Saxon hosts pull out their concealed knives, stab all the nobles to death and take Vortigern prisoner.
* OffingTheOffspring: Arthur's killing of his own son Amr. The circumstances are not explained, though.
* OneManArmy: Arthur supposedly personally killed 960[[labelnote:***]]Or [[ContinuitySnarl 940]][[/labelnote]] Saxons in the Battle of Mount Badon -- "and no one struck them down except Arthur himself", respectively:
-->''"In this engagement, nine hundred and forty fell by his hand alone, no one but the Lord affording him assistance."''
* ParentalIncest: Vortigern marries his own daughter (his third simultaneous marriage) and has a son with her.
* PoweredByAForsakenChild: When the building materials for Vortigern's fortress miraculously vanish each night, a soothsayer tells him that only by sprinkling the walls with the blood of a child without a father can break the curse, and Vortigern is ready to do that.
* RuleOfThree: UsefulNotes/JuliusCaesar invades Britain three times, and only the third times he is successful. In reality the Romans only secured Britain under the Emperor Claudius, decades after Caesar's death.
* UnaccustomedAsIAmToPublicSpeaking: Nennius -- or rather the unknown author of the preface who pretends to be Nennius -- becomes almost obnoxious with reassuring his readers that he is uneducated, ignorant of foreign languages, and utterly talentless:
-->''"Be it known to your charity, that being dull in intellect and rude of speech, I have presumed to deliver these things in the Latin tongue, not trusting to my own learning, which is little or none at all, (...) I, to this day, have hardly been able to understand, even superficially, as was necessary, the sayings of other men; much less was I able in my own strength, but like a barbarian, have I murdered and defiled the language of others. (...) But since, however, I had rather myself be the historian of the Britons than nobody, although so many are to be found who might much more satisfactorily discharge the labour thus imposed on me; I humbly entreat my readers, whose ears I may offend by the inelegance of my words, that they will fulfil the wish of my seniors, and grant me the easy task of listening with candour to my history."''
* TheUsurper: Maximus (historically better known as Magnus Maximus), who, as military commander of Britain, in 383 AD invaded Gaul to defeat and kill Emperor Gratianus, whose place he took.
* WaifProphet: Ambrosius, a child "without a father", points out to Vortigern the two dragons concealed beneath Dinas Emrys (a fact he couldn't possibly know in a natural way) and prophecies the future of Britain. The episode lived on in Arthurian lore, but from ''Literature/HistoriaRegumBritanniae'' onward, the Waif Prophet is always Myth/{{Merlin}}. ''Historia Regum Britanniae'' further says Merlin was "also known as Ambrosius".