Geoffrey of Monmouth in the context of "Layamon's Brut"

The Matter of Britain (French: matière de Bretagne; Welsh: Mater Prydain; Cornish: Mater Brythain; Breton: Afer Breizh-Veur) is the body of medieval literature and legendary material associated with Great Britain and Brittany and the legendary kings and heroes associated with it, particularly King Arthur. The 12th-century writer Geoffrey of Monmouth's Historia Regum Britanniae (History of the Kings of Britain) is a central component of the Matter of Britain.

It was one of the three great Western story cycles recalled repeatedly in medieval literature, together with the Matter of France, which concerned the legends of Charlemagne and his companions, as well as the Matter of Rome, which included material derived from or inspired by classical mythology and classical history. Its pseudo-chronicle and chivalric romance works, written both in prose and verse, flourished from the 12th to the 16th century.

The following list of legendary kings of Britain (Welsh: brenin y Brythoniaid or brenin Prydain) derives predominantly from Geoffrey of Monmouth's circa 1136 work Historia Regum Britanniae ("the History of the Kings of Britain"). Geoffrey constructed a largely fictional history for the Britons (ancestors of the Welsh, the Cornish and the Bretons), partly based on the work of earlier medieval historians like Gildas, Nennius and Bede, partly from Welsh genealogies and saints' lives, partly from sources now lost and unidentifiable, and partly from his own imagination (see bibliography). Several of his kings are based on genuine historical figures, but appear in unhistorical narratives. A number of Middle Welsh versions of Geoffrey's Historia exist. All post-date Geoffrey's text, but may give us some insight into any native traditions Geoffrey may have drawn on.

Geoffrey's narrative begins with the exiled Trojan prince Brutus, after whom Britain is supposedly named, a tradition previously recorded in less elaborate form in the 9th century Historia Brittonum. Brutus is a descendant of Aeneas, the legendary Trojan ancestor of the founders of Rome, and his story is evidently related to Roman foundation legends.

Historia regum Britanniae (The History of the Kings of Britain), originally called De gestis Britonum (On the Deeds of the Britons), is a fictitious account of British history, written around 1136 by Geoffrey of Monmouth. It chronicles the lives of the kings of the Britons over the course of two thousand years, beginning with the Trojans founding the British nation and continuing until the Anglo-Saxons assumed control of much of Britain around the 7th century. It is one of the central pieces of the Matter of Britain.

Although taken as historical truth until the 16th century, it is now considered to have no value as history. When events described, such as Julius Caesar's invasions of Britain, can be corroborated from contemporary histories, Geoffrey's account can be seen to be wildly inaccurate. It remains, however, a valuable piece of medieval literature, which contains the earliest known version of the story of King Lear and his three daughters, and helped popularise the legend of King Arthur.

Chivalry, or the chivalric language, is an informal and varying code of conduct that developed in Europe between 1170 and 1220. It is associated with the medieval Christian institution of knighthood, with knights being members of various chivalric orders, and with knights' and gentlemen's behaviours which were governed by chivalrous social codes. The ideals of chivalry were popularized in medieval literature, particularly the literary cycles known as the Matter of France, relating to the legendary companions of Charlemagne and his men-at-arms, the paladins, and the Matter of Britain, informed by Geoffrey of Monmouth's Historia Regum Britanniae, written in the 1130s, which popularized the legend of King Arthur and his knights of the Round Table.

The code of chivalry that developed in medieval Europe had its roots in earlier centuries. It arose in the Carolingian Empire from the idealisation of the cavalryman—involving military bravery, individual training, and service to others—especially in Francia, among horse soldiers in Charlemagne's cavalry. Over time, the meaning of chivalry in Europe has been refined to emphasize more general social and moral virtues. The code of chivalry, as it stood by the Late Middle Ages, was a moral system which combined a warrior ethos, knightly piety, and courtly manners, all combining to establish a notion of honour and nobility.

The historicity of King Arthur has been debated both by academics and popular writers. While there have been many claims that King Arthur was a real historical person, the current consensus among specialists on the period holds him to be a mythological or folkloric figure.

The first definite mention of Arthur appears circa 828 in the Historia Brittonum, where he is presented as a military leader fighting against the invading Saxons in 5th- to 6th-century Sub-Roman Britain at the Battle of Badon, more than three centuries before the work was written. Arthur developed into a legendary figure in the Matter of Britain from the 12th century, following Geoffrey of Monmouth's influential but largely fictional Historia Regum Britanniae.

Welsh mythology, also known as Y Chwedlau (Welsh for 'the legends'), consists of both folk traditions developed in Wales, and traditions developed by the Celtic Britons elsewhere before the end of the first millennium. As in most of the predominantly oral societies Celtic mythology and history were recorded orally by specialists such as druids (Welsh: derwyddon). This oral record has been lost or altered as a result of outside contact and invasion over the years. Much of this altered mythology and history is preserved in mediaeval Welsh manuscripts, which include the Red Book of Hergest, the White Book of Rhydderch, the Book of Aneirin and the Book of Taliesin. Other works connected to Welsh mythology include the ninth-century Latin historical compilation Historia Brittonum (History of the Britons) and Geoffrey of Monmouth's 12th-century Latin chronicle Historia Regum Britanniae (History of the Kings of Britain), as well as later Welsh folklore, such as the materials collected in The Welsh Fairy Book by William Jenkyn Thomas (1908).

Cadwaladr ap Cadwallon (also spelled Cadwalader or Cadwallader in English) was king of Gwynedd in Wales from around 655 to 664 or 682. He died in one of two devastating plagues that happened in 664 and in 682. Little else is known of his reign.

The red dragon (Welsh: y Ddraig Goch), long known as a Welsh symbol, appearing in the Mabinogion, the Historia Brittonum, and the stories of Geoffrey of Monmouth, has, since the accession of Henry VII to the English throne, often been referred to as "The Red Dragon of Cadwaladr". The association with Cadwaladr is a traditional one without any historical basis.

Brutus, also called Brute of Troy, is a mythical British king. He is described as a descendant of the Trojan hero Aeneas and as the eponymous founder and first king of Britain. This legend first appears in the Historia Brittonum, an anonymous 9th-century historical compilation to which commentary was added by Nennius, but is best known from the account given by the 12th-century chronicler Geoffrey of Monmouth in his Historia Regum Britanniae.