References to Arthur before 1100 CE.
On the Ruin and Conquest of Britain — De Excidio et Conquestu Britanniae (Latin, c510-530 CE). A sermon by the British cleric St. Gildas. It makes reference to Ambrosius Aurelianus, who in later works is the brother of Uther Pendragon, and uncle of Arthur. It also refers to the Battle of Mons Badonicus (Mt. Baden, or Bath-hill), the battle where Arthur was the war leader who lead the Britons to victory.
De Excidio et Conquestu Britanniae — Wikipedia
Gildas de excidio et conquestu britanniae — text in Latin, Keith’s history pages
On the Ruin of Britain — Project Gutenberg.
Gildas' "On the Ruin of Britain" — PDF from Camelot On-line.
Elegy for Cynddylan — Marwnad Cynddylan (Middle Welsh, c650-850 CE). Elegy to the 7th century Prince of Powys. The poem includes a very early reference to Arthur.
The line mentioning Arthur is:
I used to have brothers. It was better when they were
the young whelps of great Arthur, the mighty fortress.
Cynddylan — Wikipedia
Marwnad Cynddylan — Text in Welsh and English, Keith’s history pages
The Gododdin — Y Gododdin (Welsh, 7th–11th century CE). Ascribed to the bard Aneirin. Appears in the Book of Aneirin. Some source give what is perhaps the first mention of Arthur in literature.
The line mentioning Arthur is:
He fed black ravens on the rampart of a fortress
Though he was no Arthur.
Among the powerful ones in battle
In the front rank, Gwawrddur was a palisade.
Y Gododdin — Wikipedia
Y Gododdin — Old and Middle Welsh and Williams' translation, Project Gutenberg
Y Gododdin — Skene's translation, Celtic Literature Collective
Y Gododdin — Clancy's translation, Celtic Literature Collective
The Spoils of Annwfn — Preiddeu Annwfn (Middle Welsh, c900 CE). Attributed to Taliesin. A poem telling the tale of an expedition by Arthur and his men to Annwfn (or Annwn), likely the Otherworld, in order to steal a magical cauldron. The story may be related to later Grail stories and the Abduction of Guinevere stories.
Preiddeu Annwfn — Wikipedia
Preiddeu Annwn: The Spoils of Annwn — Sarah Higley translation, the Camelot Project. Includes both Middle Welsh and English, as well as sound files.
Preiddeu Annwn — Welsh text, Celtic Literature Collective
The Raid on the Otherworld — English trans., Celtic Literature Collective
Who is the gatekeeper? — Pa Gur yv y Porthaur (Middle Welsh, 10th century CE). This poem relates exploits of Arthur's warrior Kay. Though this is recorded in the Black Book of Carmarthen, the poem has been dated to a much earlier source.
Sir Kay, section on Pa Gur yv y Porthaur — Wikipedia
Pa Gur — Middle Welsh, Celtic Literature Collective
Arthur and the Porter — Skene's translation, Celtic Literature Collective
Culhwch and Olwen — Culhwch ac Olwen (Middle Welsh, c1080-1100 CE). Anonymous. Present in both the White Book of Rhydderch (c1325 CE) and the Red Book of Hergest (c1400 CE). This is one of the only Celtic tales that pre-dates the French romances.
Early Arthurian literature written in the form of British history.
The History of the Britons — Historia Brittonum (Latin, c828 CE). Ascribed to Nennius. The Wonders of Britain is sometimes attached to the Historia. It is a brief list of geographical wonders, including two with connections to Arthur.
Historia Brittonum — Wikipedia
Historia Brittonum — text in Latin, Keith’s history pages
Historia Brittonum — Gunn translation.
History of the Britons — Giles translation, Project Gutenberg.
Nennius' "Historia Brittonum" — PDF from Camelot On-line.
Nennius' "The Wonders of Britain" — Andy Evans' Wonders of Britain site.
The Annals of Wales — Annales Cambriae (Latin, c970 CE). Anonymous. A chronical of events in Wales and in the rest of the British isles and Ireland. Three entries relate to Arthurian legend, referring to the battles of Badon (516 CE), Camlann (537 CE), and Armterid (573 CE).
Annales Cambriae — Wikipedia
Annales Cambriae — Latin text, John Williams ed.
Annales Cambriae — translation, Celtic Literature Collective
Texts in Middle English to 1539.
Arthour and Merlin — from the Auchinleck manuscript, c.1330, National Library of Scotland (poem dated 1250–1300). IMEV 1675. DIMEV 2807. Four other manuscripts have later dates. IMEV 1162. DIMEV 1886.
Of Arthour & of Merlin — HTML transcript of the Auchinleck manuscript, National Library of Scotland.
Arthour and Merlin (Auchinleck MS), and Arthour and Merlin (Later version from Lincoln's Inn Library MS 150 and Bodleian Library Douce MS 236) — Ed. Eugen Kölbing, Altenglische Bibliothek, no. 4, 1890.
Arthour and Merlin, A Metrical Romance (Auchinleck MS and British Museum Harley 6223 MS fragment) — Ed. W. B. D. D. Turnbull, Abbotsford Club, 1838.
Merline (Percy Folio MS) — Ed. John W. Hales and Frederick J. Furnivall, Bishop Percy's Folio Manuscript: Ballads and Romances, Volume 1, 1867.
Sir Tristrem — from the Auchinleck manuscript, c.1330, National Library of Scotland (poem dated c.1300). IMEV 1382. DIMEV 2305.
Sir Tristrem — Wikipedia
Lancelot of the Laik and Sir Tristrem — Ed. Alan Lupack, TEAMS Middle English Texts Series, 1994.
Sir Tristrem — Ed. George Powell McNeill, Scottish Text Society no. 8, 1886.
Sir Tristrem in Die nordische und die englische Version der Tristan-sage. Ed. Eugen Kölbing, 1882.
Libeaus Desconus (The Fair Unknown) — from six manuscripts (before 1340). IMEV 1690, DIMEV 2824.
Libeaus Desconus — Wikipedia
Lybeaus Desconus (Lambeth Palace Library MS 306 and Biblioteca Nazionale, Naples MS XIII.B.29) — Eds. Eve Salisbury and James Weldon, TEAMS Middle English Texts Series, 2013.
Lybeaus Desconus in Codex Ashmole 61: A Compilation of Popular Middle English Verse (Bodleian Library Ashmole MS 61) — Ed. George Shuffelton, TEAMS Middle English Texts Series, 2008.
Lybeaus Desconus (British Library MS Cotton Caligula A.II) in Ancient English Metrical Romances, Volume 2 — Ed, J. Ritson, 1885.
Libeaus Desconus (edited from all manuscripts) — Ed. Max Kaluza, Altenglische Bibliothek no. 5, 1890.
Libius Disconius (Percy Folio MS) — Ed. John W. Hales and Frederick J. Furnivall, Bishop Percy's Folio Manuscript: Ballads and Romances, Volume 2, 1868.
Sir Perceval of Galles — from the Lincoln Cathedral Library 91 Robert Thornton manuscript (1320–40). IMEV 1853, DIMEV 3074.
Sir Perceval of Galles and Ywain and Gawain — Ed. Mary Flowers Braswell, TEAMS Middle English Texts Series, 1995.
Sir Perceval of Galles in The Thornton romances. The early English metrical romances of Perceval, Isumbras, Eglamour, and Degrevant — Ed. James Orchard Halliwell-Phillipps, 1844.
Sir Launfal, or Launfal Miles — by Thomas Chester from the British Library MS Cotton Caligula A.II (1320–40). IMEV 567, DIMEV 930.
Sir Launfal in The Middle English Breton Lays — Ed. Anne Laskaya and Eve Salisbury, TEAMS Middle English Texts Series, 1995.
Launfal, An Ancient Metrical Romance — Ed. Joseph Ritson, 1891.
Arthur — from Longleat House MS 55 (1350–1400). IMEV 1113, DIMEV 1794.
Arthur: A Short Sketch of His Life and History — Ed. Frederick J. Furnivall, Early English Text Society, Orig. Series no. 2, 1864.
Sir Gawain and the Green Knight — from the Cotton Nero A.x. manuscript (late 14th century). IMEV 3144. DIMEV 4920.
Sir Gawain and the Green Knight — Wikipedia
Sir Gawain and the Green Knight manuscript facsimile — University of Calgary Digital Collections
Sir Gawain and the Green Knight — Ed. J. R. R. Tolkien and E. V. Gordon, 1925, rev. Norman Davis, 1967. This is an HTML transcript.
Sir Gawayne and the Green Knight — Ed. Richard Morris, Early English Text Society, Orig. Series no. 4, 1864, rev. 1897 and 1912 by I. Gollancz.
Stanzaic Morte Arthur — from the British Museum Harley 2252 manuscript (c.1400). IMEV 1994. DIMEV 3252.
Stanzaic Morte Arthur — Wikipedia
King Arthur's Death: The Middle English Stanzaic Morte Arthur and Alliterative Morte Arthure — Ed. Larry D. Benson, TEAMS Middle English Texts Series, 1994.
Le Morte Arthur, A Romance in Stanzas of Eight Lines — Ed. J. Douglas Bruce, Early English Text Society, Extra Series no. 88, 1903.
Alliterative Morte Arthure — from the Lincoln Cathedral Library 91 Robert Thornton manuscript (c.1400). IMEV 2322. DIMEV 3745.
Alliterative Morte Arthure — Wikipedia
King Arthur's Death: The Middle English Stanzaic Morte Arthur and Alliterative Morte Arthure — Ed. Larry D. Benson, TEAMS Middle English Texts Series, 1994.
Morte Arthure, or The Death of Arthur — Ed. Edmund Brock, Early English Text Society, Orig. Series no. 8, 1865, rev. 1871.
Morte Arthur, Two Early English Romances — Ed. Ernest Rhys, 1912. A modern translation.
Prose Merlin — from the Cambridge University Library MS Ff.3.11. (c.1450).
Prose Merlin — Ed. John Conlee, TEAMS Middle English Texts Series, 1998.
Merlin, or the Early History of King Arthur [Vol 1] [Vol 2 & 3] [Vol 4] — Ed. Henry B. Wheatley, Early English Text Society, nos. 10, 21, 36, 112, 1865–1899.
HTML transcript of text — Corpus of Middle English Prose and Verse
Le Morte d'Arthur — by Sir Thomas Mallory (c.1468).
Le Morte d'Arthur — Wikipedia
The Winchester Manuscript of Le Morte d'Arthur — The earliest form of the work as a handwritten manuscript. It was discovered in Winchester Library in 1934. The manuscript starts at the obverse side of folio 9. This corresponds to page 20, line 23 in Vinaver's edition below.
The Works of Sir Thomas Malory [Vol 1] [Vol 2] [Vol 3] — Ed. Eugène Vinaver, 1947. 3 vol. The first printed edition of the Winchester manuscript version of Mallory. This is a more critical edition than those that followed.
The Byrth, Lyf, and Actes of Kyng Arthur [Vol 1] [Vol 2] — Ed. T. Davison, 1817. An early modern version of Caxton's 1485 printed edition, with original spelling. All subsequent editions, including those with modern spellings, were based on this edition until the discovery of the Winchester manuscript.
Le Morte Darthur, Volume 1: Text — Ed. H. Oskar Sommer, 1889. A formatted version of Caxton, with original spelling. [Vol. 2: Introduction] [Vol. 3: Studies on the Sources]
[HTML transcript of Vol. 1]
La Morte Darthur [Vol 1] [Vol 2] [Vol 3] [Vol 4] — Ed. Israel Gollancz, 1897. This edition, with modern spelling, was illustrated by Aubrey Beardsley.