In past blog posts, I discussed various possible 'Llydaws' in or adjacent to Wales that could have been used as substitutes for Llydaw or Brittany proper. Among these are the Vale of Leadon, which borders on the ancient Welsh kingdom of Ercing, as well as a possible identification with the Ui Liathain territory in Co. Cork (Munster).
Here I wish to confine myself to an actual known Llydaw in Wales - Llyn Llydaw, a large lake in Arfon, Gwynedd.
I had not paid much attention to this location in the past - and possibly to my detriment. For Llyn Llydaw is not only a mere half dozen kilometers from Dinas Emrys, it is the feeder lake for the river that empties into Llyn Dinas at the foot of this hillfort. I'm attaching here some maps that nicely show the geographical proximity and relationship of these sites.
We will recall that Geoffrey of Monmouth has Constantine and his sons, Aurelius Ambrosius and Uther Pendragon, come to Britain from Brittany (or Llydaw). Discount Geoffrey's clumsy (or ingenious) conflation of Ambrosius and the Northern Merlin (Myrddin) at Dinas Emrys. Never mind that hillfort's further confusion with Amesbury near Stonehenge in Wiltshire. If we stick with pre-Galfridian tradition (Nennius), Ambrosius Aurelianus is given Dinas Emrys by Vortigern, along with all the kingdoms of the western part of Britain, i.e. Gwynedd.
Suppose, hypothetically speaking, we allow for Uther Pendragon coming to southern Wales from Dinas Emrys in "Llydaw"?
At one time or another I've tried to make a case for Uther being either a title for Ambrosius himself (an unhelpful identification, as Ambrosius belongs to the 4th century and was never even in Britain!) or for the great Cunedda. If we place Ambrosius at Dinas Emrys, does this help us any in our quest for the Terrible Chief Dragon?
Yes - perhaps. But not in the way we may wish it to!
Dinas Emrys was in Eryri, and I've explained in the past how this mountain-name could easily have been confused for the Welsh word for eagle. The same was true of Aquileia on the Continent (easily associated with Latin aquila), and so a whole bunch of famous Roman emperors and peripheral figures get relocated to Dinas Emrys in legend. St. Ambrose (namesake of his father, a Governor of Gaul) is found there, as is Magnus Maximus (called Maximo tyranno in the HISTORIA BRITTONUM, a name/title that could easily have been associated with Vor-tigern). Maximus is executed at Aquileia. The usurper Eugenius was killed near Aquileia (probably this is the Owain Finddu son of Maximus at Dinas Emrys). Constantine II was killed at Aquileia, and we know Gratian was there, too. The HISTORIA BRITTONUM tells us that St. Martin spoke with Maximus (see http://www.livius.org/sources/content/martinus-of-tours-and-maximus/). If Myrddin was linked by Geoffrey of Monmouth with Martin, this may be one reason why he chose to identify Myrddin/Merlin with Ambrosius at Dinas Emrys. Constantius II captured Aquileia, and forces loyal to the future pagan emperor Julian (who was intimately associated with the draco and the dragon) laid siege to the city.
Ambrosius Aurelianus himself, as the 'Divine/Immortal Golden One', came to be identified with the god Lleu, made Lord of Gwynedd in Welsh story. Lleu is found in eagle form in Nantlle in Eryri. A.A. as a fatherless boy in the ballgame at Campus Elleti is a motif borrowed from the story of the Irish god Mac Og, 'Young Son.' In Welsh tradition, Mabon and Lleu are identified, as both are placed in Nantlle in death. This identification of A.A. with Lleu/Mabon may have eased the former's identification with the Northern Myrddin (Merlin), who has strong Lleu affinities.
In short, the legends surrounding Dinas Emrys are a tangled mess. According to Bartram, Arfon (in which Dinas Emrys was situated) was not a part of the original occupied territory of Cunedda and his sons. Pasted here is the relevant section from A CLASSICAL WELSH DICTIONARY:
"The ‘Harleian’ genealogies supplement this (HG 32, 33 in EWGT p.13) as follows:
These are the names of the sons of Cunedda, whose number was nine:  Tybion, the first-born,
who died in the region called Manaw Gododdin and did not come hither with his father and his
aforesaid brothers. Meirion, his son, divided the possessions among his [Tybion's] brothers. 2.
Ysfael, 3. Rhufon, 4. Dunod, 5. Ceredig, 6. Afloeg, 7. Einion Yrth, 8. Dogfael, 9. Edern.
This is their boundary: From the river which is called Dyfrdwy [Dee], to another river, the Teifi;
and they held very many districts in the western part of Britain.
A similar account is given in the second Life of St.Carannog (§§2, 3 in VSB 148) except that the
southern boundary is made the Gwaun instead of the Teifi. The secular boundary of Ceredigion was
always the Teifi. The variant version is due to the fact that the Archdiaconical region was later extended to the Gwaun, so that it included part of Dyfed (VSB pp.xi-xii).
All the sons of Cunedda listed above, except Tybion and Einion Yrth, gave their names to the
kingdoms which were allotted to them, namely, Ysfeilion, Rhufoniog, Dunoding, Ceredigion, Afloegion, Dogfeiling and Edeirnion; Meirion, son of Tybion, gave his name to Meirionydd, and Einion's kingdom appears to have been Rhos.
The sons of Cunedda thus held the north and west coastal districts of Wales, from the mouth of
the Clwyd to the mouth of the Teifi, with the exception of Llyn, Arfon, Arllechwedd, and most of
Anglesey. These seem to have been conquered later by Cadwallon Lawhir ab Einion Yrth. The position of these conquests suggests that entry was made by the sea. (A.W.Wade-Evans in Arch.Camb., 85 (1930) p.333); WCO 39, 88)...
To Cadwallon [born c. 440 A.D.], who was probably not the eldest son, it fell to extend the dominions of the family in Arfon and to conquer the greater part of Môn from the Irish inhabitants [Gwyddyl]. This can be gathered from relatively late traditions. A great battle was fought at a place called Cerrig-y-Gwyddyl in Môn, and Cadwallon's war-band tied the fetter-locks of their horses to their own feet [lest they should waver] in the fight against Serigi Wyddel, so that they are called one of the ‘Three Fettered War-Bands’ of Ynys Prydain (TYP no.62). Cadwallon was aided in the battle by his three cousins, Cynyr, Meilir and Yneigr, sons of Gwron ap Cunedda. Cadwallon slew Serigi at a place called Llam-y-Gwyddyl, ‘the Irishmen's Leap’, in Môn (ByA §29(15) in EWGT p.92). Some later versions mistakenly write Caswallon and Llan-y-Gwyddyl."
The irony here, of course, is that Cunedda came from Ireland (see my previous books and many articles), and his sons were either Irish themselves or Hiberno-British. They may have chased out the Laigin (a tribal name preserved in that of Dinllaen and Lleyn). But any conquest inland, including the region of Dinas Emrys in Arfon, would have been at the expense of native Britons.
What all of this tells me is that I might well have been right, all those years ago, when I proposed, only half-seriously, that Uther Pendragon was merely a title for Ambrosius Aurelianus. This latter "fictional" chieftain of Dinas Emrys was said to be (HB Chapter 48) rex magnus or the 'great king' among the Britains. His fort was that of the Red Dragon, symbolic of the British, so he was the de facto pen or "chief" of that particular beast. Also, Vortigern was said to have 'timore Ambrosii', dread of Ambrosius. One of the meanings of Uther (see GPC) is 'dreadful'. It was not difficult to see in this combination of facts the title Uther Pendragon.
To quote from Bruce's THE ARTHURIAN NAME DICTIONARY:
"After Geoffrey's chronicle, Ambrosius disappears from legend and romance for some time. The authors of the Prose Merlin and the Vulgate Cycle renamed him Pendragon [emphasis mine]. He resurfaces in the seventeenth century..."
Now, partly this can be explained by the Galfridian fusion of Ambrosius and Merlin at Dinas Emrys. As Merlin now played a prominent role, that of Ambrosius would naturally have been downplayed or even to have disappeared. However, it does not account for why the Pendragon epithet continued to be used as a separate character, and one plainly based on Ambrosius. Instead, this would seem to be confirmation of my idea that Ambrosius IS Uther Pendragon.
My reluctance to adhere to this notion had to do with my desire (not unique among Arthurian scholars) to identify Uther with a chieftain who could actually be Arthur's father. And that desire, I now feel, has led me seriously astray.
The only way for me to explain the Arthur name and his undeniable connection with the Irish, as well as the locations of his battles, is to remain faithful to the theory propounded in my book THE BEAR KING, i.e. that Arthur is a decknamen for either Irish Artri or British Arthr(h)i, 'Bear-king', and that this title was applied to Ceredig son of Cunedda (= Cerdic of Wessex).
That Uther is said to have come from the Llydaw in Arfon would be correct in one sense only: the descendants of Cunedda, father of Ceredig/Arthur, had conquered and settled that region early on. As the progenitor of the princes of Gwynedd, Cunedda was the true Terrible Chief Dragon.