The Boar Hunting Party
In Culhwch And Olwen, considered the oldest Arthurian tale, Culhwch invokes almost 260 personages as guarantors of the privileged gift, or boon, which he demands on recognition of his kinship as Arthur's first cousin, symbolised by the act of Arthur cutting Culhwch's hair. Culhwch demands 'My claim on thee is that thou get me Olwen daughter of Ysbaddaden Chief Giant. And I invoke her in the name of thy warriors.' 
Culhwch's extensive invocation of individuals from Arthur's Court, occupying over two hundred lines in the tale, draws upon the names of both historical and mythological British personages and a lesser number of Irish, in addition to a number of obviously invented farcical characters. Many appear here for the first time and are unknown outside Culhwch. Some fail to appear again in the tale and other characters are introduced later who do not appear in the list. Thus, this so-called 'Court List' contains an accumulation of Celtic literary figures unique to Culhwch, probably added to at each recital and by later copyists.
The Chief Giant Ysbaddaden exacts forty impossible tasks, or 'anoethau', from Culhwch as the price for obtaining his daughter Olwen as his wife. Achieving the anoethau constitutes the rest of the tale, with the most important, and central to the whole story, is the hunting of the enchanted giant boar, the Twrch Trwyth. The hunt begins in Ireland and Arthur and his retinue follow the boar across the Celtic Sea to south Wales.
Four of Arthur's champions killed by the Twrch Trwyth at Cwm Cerwyn, Pembrokeshire, south west Wales, are referred to in the passage from Culhwch And Olwen cited above. Tarawg of Allt Clwyd is previously unmentioned, Rheiddwn son of Eli Adfer, and Isgofan the Generous appear to have been transplanted from the Court List with no further references. However, the fourth champion Gwarthegydd appears from the long tradition of the sons of Caw of Prydyn (Pictland). The Court List mentions nineteen sons of Caw but omits Gwarthegydd ('cattle raider'). The inclusion of Gwarthegydd concurs with early Welsh genealogical tradition that lists twenty sons of Caw, including Gildas and Hueil, and one daughter. Outside of Culhwch, Gwarthegydd son of Caw is found seated next to Bedwini, the Bishop, as part of the assemblage of Arthur's counsel in the late 13th century Middle Welsh tale The Dream of Rhonabwy.
The Stones of the Sons of Arthur
According to local lore the site of the battle of Cwmcerwyn is marked by a series of ancient monuments. Legend recalls that Arthur sat and watched his men fighting the Twrch Trwyth from a spot marked by a standing stone known as Eisteddfa Arthur (Arthur's Seat), slightly north of Brynberian, on the northern side of the main ridge of the Preseli Hills.
The Stones of the Sons of Arthur are located on the lower flank of Foel Cwmcerwyn, the highest top in the Preselis at 1760ft (537m) and the source of the Afon Clydach. On the ridge above are said to be The Stones of the Knights, (Cerrig Marchogion - SN102322). 
The Stones of the Knights are difficult to locate, if they survive at all today, and I suspect the four ancient cairns, the highest at 5ft tall, seen prominently along the skyline of Foel Cwmcerwyn, were probably the original draw to the legend of Arthur's battle with the Twrch Trwyth, as often they are called by the alternative name of The Stones of Arthur's Knights, no doubt commemorating Arthur's four champions, Gwarthegydd, Tarawg, Rheiddwn and Isgofan that the giant boar killed here. The western most cairn was excavated in the early nineteenth century, uncovering a typical Early Bronze Age cremation in an inverted urn. However, the other cairns appear to be empty.
The next site marking the continuing battle with Twrch Trwyth is marked by The Stones of the Sons of Arthur (Cerrig Meibion Arthur – SN118310), where two erect stones stand about 8m apart, some140m south-east of Ty Newydd farm in Cwm Cerwyn, Mynachlog-ddu, on the southern side of the Preseli Hills. The stones are said to be a monument to Arthur's sons killed here by the Twrch Trwyth which had swum over from Ireland.
The Stones of the Sons of Arthur are part of the Glynsaithmaen group of standing stones located in the moorland around Ty Newydd farm in the hollow beneath Foel Cwmcerwyn in the boggy ground near the headwaters of Afon Wern. The name 'Glynsaithmaen', (valley of the seven stones), suggests the group originally consisted of seven monoliths or seven arrangements of stones, only six are obvious today, although other large stones in and around the farm and track behind the The Stones of the Sons of Arthur possibly account for the seventh. Alternatively, it has been suggested that the name may refer to certain stones considered particularly potent for arrow sharpening.
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The Sons of Arthur
The boar hunt in Culhwch recalls only one son of Arthur, Gwydre, yet here we find two large standing stones. In Welsh tradition Arthur has three sons, Llachau and Amr completing the trio. We know from the Mirabilia (Marvels, or Wonders of the Island of Britain) appended to the 9th century Historia Brittonum that Amr's tomb is to be found at the source of the river Gamber, the spring called Llygad Amr (the eye of Amr) in the district of Ercing (Archenfield, near Hereford):
"There is another miracle in the region which is called Ercing. A sepulcra is shown near a spring which is given the name Licat Amr, and the name of the hero who's grave is in the tumulus, it follows, was called Amr. He was the son of Arthur the soldier, and he himself has killed him in that very place and done the burying. And men come to measure the tumulus in length: sometimes it is six feet; sometimes nine; sometimes twelve; sometimes fifteen. For whatever the measurement you will measure it in such a succession, again you will not find it with the same measurement; and even I have made confirmation on my own."
Isgawyn son of Banon has been compared with the name Kysceint mab Banon who appears in the incomplete poem Pa Gur? (from the first line Pa Gur yv y Portaur - 'What man is the porter?') found in the The Black Book of Carmarthen.  This early Arthurian poem, usually dated to the 11th century, begins as a dialogue between Arthur and Glewlwyd, the porter or gate-keeper, and develops into a list of Arthur's retinue and their feats, with many of the names and references being similar to those found in Culhwch and Olwen, suggesting a common early source for the two works. 
Arthur's son Llachau is mentioned in Pa Gur? Considering the similarity between the Black Book poem and Culhwch it seems odds that Llachau does not appear in the later.
“Cei the fair and Llachau,
they performed battles
before the pain of of blue spears (ended the conflict)” 
In later Medieval Romance Kay murders a son of Arthur called Loholt, which has been interpreted that Cei must have killed Llachau. Yet the passage above from Pa Gur? seems to suggest that Cei and Llachau fought on the same side.
Another poem from the Black Book of Carmarthen, The Dialogue of Gwyddneu Garanhir and Gwyn ap Nudd, refers to Llachau's death, and at first glance the passage fails to provide the location:
“I have been where Llacheu was slain, son of Arthur marvellous in song, when ravens croaked over his blood.”
Only six stanzas previous the poem recalls a battle before Caer Vandwy,  an Otherworld fortress. Assuming the poem follows sequential events, it is reasonable to expect Llacheu's death to have followed the assault on Caer Vandwy. The only other early Welsh poem to name this fortress is the Spoils of Annwn, recalling Arthur's raid on the Otherworld.  Considering that the theme of the raid on the Otherworld is common to Culwch and Spoils of Annwn with similar elements appearing in the poem Pa Gur? we should therefore expect to see Llachau in Culhwch. We can therefore deduce that Llachau's death occurred after the journey to the Otherworld. In Culhwch the Otherworld is euphemised as Ireland; significantly Arthur's son(s) are killed in south-west Wales after pursuing the Twrch Trwyth from Ireland.
Further, there is a reference to Llachau in the early Triad, Three Well-Endowed Men of the Island of Britain:
'Gwalchmai son of Gwyar,
and Llachau son of Arthur,
and Rhiwallawn Broom-Hair'
Gwalchmai belongs to the earliest stratum of the Arthurian legend and appears along with Cei and Bedwyr in Culhwch. Lllachau appears along with Cei in Pa Gur? Coupled with this early Triad it is apparent that Llachau belongs to the earliest part of the Arthurian mythos. According to a poem in the Black Book of Carmarthen, Llachau dies following a journey to the Otherworld. The second monolith of The Stones of the Sons of Arthur must surely mark the spot where Llachau, along with Gwydre, was killed by the Twrch Trwyth.
|Cerrig Meibion Arthur|
Arthur's son Gwydre is not mentioned in the Court List, but we do find a Gwydre son of Llwydeu by Gwenabwy daughter of Caw. Significantly, Gwydre son of Llwydeu is not mentioned again in Culhwch, the name Gwydre appears but once more in the whole tale; at the battle of Cwm Cerwyn.
Is this the same character? If so he must be of questionable parentage. The apparent insignificance of Gwydre's passing has led to suggestions that he was illegitimate.  And there may be good reason to accept this claim.
Gwenabwy is the sole daughter of Caw mentioned in the Court List. According to this list she has a son, Gwydre, by Llwydeu son of Nwython. The Saints Lives alludes to a tradition of hostility between Arthur and the Pictish warrior Hueil. Caradoc of Llancarfan's Vita Gildae (Life of Gildas) describes Hueil as an "active warrior and most distinguished soldier", who led a number of violent and sweeping raids from north of the Wall plundering Arthur's lands.
In Culhwch, Hueil is said to have never submitted to a lord's hand and the enmity between him and Arthur is further alluded to in the Court List which refers to an incident in which Hueil stabbed his nephew, Gwydre son of Llwydeu. The ensuing feud between Arthur and Hueil ended in the death of the latter suggesting Gwydre was more than simply Arthur's nephew. It is possible that Gwydre son of Llwydeu was identical with Gwydre son of Arthur, implicative of Arthur's infidelity with Gwenabwy, daughter of Caw.
The Medieval historian Gerald of Wales claims Gildas threw all mention of Arthur in his books into the sea because he killed his brother Hueil.
Notes & References:
1. Culhwch And Olwen, from The Mabinogion, by Gwynn Jones & Thomas Jones, 1949.
3. Chris Barber & John Godfrey Williams, The Ancient Stones of Wales, Blorenge, 1989.
4. Rachel Bromwich & D Simon Evans, Culhwch and Olwen, University of Wales Press, 1992.
5. Patrick Sims Williams, The Early Welsh Arthurian Poems, in Arthur of the Welsh, ed. Bromwich et al.1991
7. Translated as 'Fortress of God's Peak' by Sarah Higley, text and translation, Preiddeu Annwn: "The Spoils of Annwn", at The Camelot Project, or 'the Fort of the Divine Place' by John T Koch & John Carey, The Celtic Heroic Age, Celtic Studies Publications, 4th revised edition, 2003.
8. Thomas Green, Concepts of Arthur, Tempus, 2007.
9. Norris J Lacy, The Arthurian Handbook, Garland, 1988.
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