Manuscripts
Manuscript:
Aberystwyth, National Library of Wales, Peniarth MS 1 = Black Book of Carmarthen (Llyfr Du Caerfyrddin)
  • c. 1250
Jones, Nerys Ann [ed.], Arthur in Welsh poetry, MHRA Library of Medieval Welsh Literature 4, Cambridge: Modern Humanities Research Association, 2019.  
abstract:
For over a thousand years, Arthur has had widespread appeal and influence like no other literary character or historical figure. Yet, despite the efforts of modern scholars, the earliest references to Arthurian characters are still shrouded in uncertainty. They are mostly found in poetic texts scattered throughout the four great compilations of early and medieval Welsh literature produced between 1250 and 1350. Whilst some are thought to predate their manuscript sources by several centuries, many of these poems are notoriously difficult to date. None of them are narrative in nature and very few focus solely on Arthurian material but they are characterised by an allusiveness which would have been appreciated by their intended audiences in the courts of princes and noblemen the length and breadth of Wales. They portray Arthur in a variety of roles: as a great leader of armies, a warrior with extraordinary powers, slayer of magical creatures, rescuer of prisoners from the Otherworld, a poet and the subject of prophecy. They also testify to the possibility of lost tales about him, his father, Uthr, his son, Llachau, his wife, Gwenhwyfar, and one of his companions, Cai, and associate him with a wide array of both legendary and historical figures. Arthur in Early Welsh Poetry, the fourth volume in the MHRA Library of Medieval Welsh Literature series, provides discussion of each of the references to Arthurian characters in early Welsh poetic sources together with an image from the earliest manuscript, a transliteration, a comprehensive edition, a translation (where possible) and a word-list. The nine most significant texts are interpreted in more detail with commentary on metrical, linguistic and stylistic features.
[1] “The Black Book of Carmarthen”
Williams, Myriah, “Ys celuit ae dehoglho: interpreting a dream?”, North American Journal of Celtic Studies 1:2 (November, 2017): 121–150.  
abstract:
The second poem in the Black Book of Carmarthen (NLW Peniarth MS 1) is known by its first line as Breuddwyd a welwn neithiwr ‘I had a dream last night’. This poem is incomplete due to the loss of a leaf or, more probably, a quire, and it is the only poem in the Black Book which A. O. H. Jarman did not fit into a category in his edition of the manuscript. Indeed, the poem has been little studied, with discussion generally amounting to a passing reference to the form of the work being a list of metricized proverbs. It is this disconnect between a poem which purports, or is purported, to be about a dream, but that is said to be composed of proverbs, which has led to difficulties in its categorization, and it is this same disconnect which is immediately interesting. By breaking the verse down into its constituent parts, it is possible to argue that the poem as it now stands is a composite work and that, at its core, there is a coherent proverbial poem around which marginal verses were accumulated through several stages of copying. The first part of this paper seeks to explore this possibility, while the second part presents a discussion of the potential relationship between Breuddwyd a welwn neithiwr and later proverb lists.
Bollard, John K. [ed. and tr.], and Anthony Griffiths [ill.], Englynion y beddau: The stanzas of the graves. Verses on the legendary heroes of Wales from The Black Book of Carmarthen, Llanrwst: Gwasg Carreg Gwalch, 2015.  
Text edition in modern Welsh orthography, with English translation, notes and commentary (Bollard); with photographic illustratations of the places mentioned in these verses (Griffiths).
Russell, Paul, “Scribal (in)consistency in thirteenth-century South Wales: the orthography of the Black Book of Carmarthen”, Studia Celtica 43 (2009): 135–174.
Sims-Williams, Patrick, “The early Welsh Arthurian poems”, in: Bromwich, Rachel, A. O. H. Jarman, and Brynley F. Roberts (eds.), The Arthur of the Welsh. The Arthurian legend in medieval Welsh literature, Arthurian Literature in the Middle Ages 1, Cardiff: University of Wales Press, 1991. 33–71.
Strachan, John, “On some mutations of initial consonants in the Old Welsh verb”, Ériu 3 (1907): 20–28.
Internet Archive: <link>
Evans, J. Gwenogvryn, Report on manuscripts in the Welsh language, vol. 1:2: Peniarth, Historical Manuscripts Commission, London, 1899.
Internet Archive: <link>
297   “MS 1”
Hengwrt MS 11 (Black Book of Carmarthen)