Geoffrey of Monmouth's Historia Regum Britanniae (English: The History of the Kings of Britain) is a pseudohistorical account of British history, written around 1136. It chronicles the lives of the kings of the Britons in a chronological narrative spanning a time of two thousand years, beginning with the Trojans of Homer's Iliad founding the British nation and continuing until the Anglo-Saxons assumed control of Britain around the 7th century. It is one of the central pieces of the Matter of Britain.
It has virtually no value as history—when events described, such as Julius Caesar's invasions of Britain, can be corroborated from contemporary histories, Geoffrey's accounts can be seen to be wildly inaccurate—but is a valuable piece of medieval literature, which contains the earliest known version of the story of King Lear and his three daughters, and introduced non-Welsh-speakers to the legend of King Arthur.
The Historia begins with the Trojan Aeneas, who according to Roman legend settled in Italy after the Trojan War. His great-grandson Brutus is banished, and, after a period of wandering, is directed by the goddess Diana to settle on an island in the western ocean, which he names "Britain" after himself.
The story continues chronologically, taking in such rulers as Bladud, who uses magic and even tries to fly; Leir, who divides his kingdom among his three daughters according to how much they profess to love him, a story which Shakespeare used as the basis of his tragedy King Lear; and Dunvallo Molmutius, who codifies the Molmutine Laws. Dunvallo's sons, Belinus and Brennius, fight a civil war before being reconciled, and proceed to sack Rome (based on the sack of Rome in 390 BC by the Gallic leader Brennus).
Caesar's invasions of Britain are opposed by Cassibelanus. There is a brief notice of a king called Kymbelinus, on whom Shakespeare based his play Cymbeline. Then Claudius invades, opposed by Kymbelinus's sons Guiderius and Arvirargus. The line of British kings continues under Roman rule, and includes Lucius, Britain's first Christian king, and several Roman figures, including the emperor Constantine I, the usurper Allectus and the military commander Asclepiodotus.
After the Romans leave, Vortigern comes to power, and invites the Saxons under Hengist and Horsa to fight for him as mercenaries, but they rise against him, and Britain remains in a state of war under Aurelius Ambrosius and his brother Uther Pendragon, assisted by the wizard Merlin. Uther's son Arthur defeats the Saxons so severely that they cease to be a threat until after his death. In the meantime, Arthur conquers most of northern Europe and ushers in a period of peace and prosperity that lasts until the Roman emperor Lucius Tiberius demands that Britain once again pay tribute to Rome. Arthur defeats Lucius in Gaul, but his nephew Modred seizes the throne in his absence. Arthur returns and kills Modred, but, mortally wounded, he is carried off to the isle of Avalon, and hands the kingdom to his cousin Constantine.
With Arthur gone, the Saxons return, and become more and more powerful. The line of British kings continues until the death of Cadwallader, after which the Saxons – the English – are the rulers of Britain.
Geoffrey claimed to have translated the Historia into Latin from "a very ancient book in the British tongue", given to him by Walter, Archdeacon of Oxford, but few scholars take this claim seriously. Much of the work appears to be derived from Gildas's 6th century polemic The Ruin of Britain, Bede's 8th century Ecclesiastical History of the English People, the 9th century History of the Britons ascribed to Nennius, the 10th century Welsh Annals, medieval Welsh genealogies and king-lists, the poems of Taliesin, the Welsh tale Culhwch and Olwen, and some of the medieval Welsh Saint's Lives, expanded and turned into a continuous narrative by Geoffrey's own imagination.
The history of Geoffrey forms the basis for much English lore and literature as well as being a rich source of material for Welsh bards. It became tremendously popular during the High Middle Ages, revolutionising views of British history before and during the Anglo-Saxon period despite the criticism of such writers as William of Newburgh and Gerald of Wales. The prophecies of Merlin in particular were often drawn on in later periods, for instance by both sides in the issue of English influence over Scotland under Edward I and his successors.
The Historia was quickly translated into Norman French verse by Wace (the Roman de Brut) in 1155; into Middle English verse by Layamon (the Brut) in the early 13th century; and into three different Welsh prose versions by the end of the 13th century. One of these Welsh translations, the so-called Brut Tysilio, was proposed in 1917 by the archaeologist Sir William Flinders Petrie to be the ancient British book that Geoffrey translated, although the Brut itself claims to have been translated from Latin by Walter of Oxford, based on his own earlier translation from Welsh to Latin.
For many centuries, the Historia was accepted at face value, and much of its material was incorporated into Holinshed's 16th century Chronicles.
Modern historians have regarded the Historia as a work of fiction with some factual information contained within. John Morris in The Age of Arthur calls it a "deliberate spoof," although this is based on misidentifying Walter, archdeacon of Oxford, as Walter Map, a satirical writer who lived a century later.
Manuscript tradition and textual history
Almost two hundred medieval manuscripts of the Historia survive, dozens of them copied before the end of the twelfth century. Even among the earliest manuscripts a large number of textual variants, such as the so-called 'First Variant', can be discerned. These are reflected in the three possible prefaces to the work and in the presence or absence of certain episodes and phrases. Certain variants may be due to 'authorial' additions to different early copies, but most probably reflect early attempts to alter, add to or edit the text.
Unfortunately, the task of disentangling these variants and establishing Geoffrey's original text is long and complex, and the extent of the difficulties surrounding the text has been established only recently.