"I am not aware of any proven case of cutting of -al in particular for the purpose of forming a hypocoristic. One problem aside, namely that hypocoristics are more usually formed with a dedicated suffix (such as frequently -án, if not the older -u), another difficulty is that after “shortening”, it is generally impossible to ascertain what the lost second part was, unless there happens to be only one name in existence with that first part. A typical case to illustrate my point is Cathán, which in view of the popularity of cath in names could formally represent any one of Cathal, Cathgal, Cathgus, etc. And on top of that there is also the unshortened Cathalán, which could suggest (a full and much more time-consuming analysis of the material pending) that hypocoristic loss of -al was actually avoided.
And for the present case, an added difficulty is that Welsh Daeth is actually a poor fit even for *Dath/*Daith by itself because of the diphthong -ae-."
Math Son of Mathonwy Sites in Relation to Dinas Emrys
If a case cannot be made for Caer Dathal being another name for Din Daethwy, where is the former fort?
One clue remains. Arthur is said to be related to the sons of Iaen, who occupy Caer Dathal. But Iaen is not a true personal name. It is, instead, the Welsh word for ice or, more specifically, an ice sheet and, by extension, a glacier. While it is certainly possible Iaen is a corruption of a real personal name (perhaps an Irish one), the Mabinogion stories are replete with such made-up personal names. If we go with Iaen as a designation for someplace in Arfon dominated by ice, then we must look to that part of Arfon that included Snowdonia/Eryri.
In previous blog posts I showed that there never was an Ambrosius at Dinas Emrys. Nor is it likely the hillfort was ever really called after Vortigern as the "Fiery Pharoah". The story of the High King giving Dinas Emrys and Gwynedd to Ambrosius was clearly substituted for what really happened, i.e. the northwestern part of Wales was given to or taken by the Irish. There is ample evidence to support this claim, from Laigin place-names to the advent of Cunedda (a chieftain of the Ciannachta).
Dinas Emrys is not only in Arfon, but in Eryri. It lies in a location that, during hard winters, becomes an ice-laden landscape. A fort in such a place might well have been poetically termed the home of the "Sons of Ice". Dinas Emrys is also well-situated in regards to the other places that figure in the Math Son of Mathonwy tale (see the map above).
Could it be, then, that the reason Caer Dathal - such a famous place in the ancient lore of Wales - became lost is solely because its Irish nature had been concealed beneath the name of the legendary Ambrosius, last of the Romans in Britain? Was it an Irish chieftain by the name of Dathal who was responsible for the proven sub-Roman occupation of Dinas Emrys?
I've long been frustrated with the Emrys story. I knew that something else was there - but I couldn't find anything beneath the folklore accretions. But if we accept as fact that it was not Ambrosius who took or was granted Gwynedd, but instead the Irish, then it stands to reason that Dinas Emrys itself must once have had an Irish name.
And the Dathal of Caer Dathal is just such a name.
If Iaen ("ice") is indeed an indicator that the fort was in the mountains of Arfon, then all the various lowland forts that have been proposed for it can no longer be considered. While other forts exist in Snowdonia, none - to my knowledge - display evidence of Dark Age occupation.
THE SONS OF IAEN
Here is the entry on Iaen from P.C. Bartram's A CLASSICAL WELSH DICTIONARY:
A list of the sons of Iaen, supposed to be present at Arthur's Court, is given in the tale of
‘Culhwch and Olwen’ (WM 461, RM 107). Their names are:
Teregud, Sulien, Bradwen, Morien, Siawn, and Caradog,
and they are said to be men of Caer Dathal, kindred to Arthur on his father's side, or perhaps ‘on their
father's side’ (CO(2) p.77).
In the ‘Hanesyn Hen’ tract there is a list of the children of Iaen as follows (ByA §2 in EWGT
Dirmig Corneu, Gwyn Goluthon, Siawn, Caradog, Ievannwy, Llychlyn, and a daughter, Eleirch*,
mother of Cydfan ab Arthur.
Note that only two names, Siawn and Caradog, are common to the two lists.
Garthiaen** is a township in the parish of Llandrillo-yn-Edeirnion (WATU). Caer Dathal is
presumably Caer Dathyl in Arfon mentioned in the Mabinogi branch of ‘Math’ (WM 81, RM 59). On
the site see W.J.Gruffudd, Math vab Mathonwy, 1928, pp.343-4; PKM p.251.
* There is a town called Eleirch (now Elerch) on the Afon [E]Leri in Ceredigion. The wife of Ceredig son of Cunedda, my candidate for Arthur, is one Meleri, or 'My Eleri', which I've suggested is the divinized form of the river.
**I would add that there is an Afon Iaen in Montgomeryshire.