According to Blake and Lloyd, Geoffrey and the Brut name three seas of Britannia/Ynys Pridein, implying that they name them as a discrete traditional group, in the manner of Trioedd Ynys Prydein (‘The Triads of Ynys Prydein’). In fact, they name them only in passing. The Sea of Caithness is named in HRB ix.1 and possibly in iii.5, where the mention of a ‘shore’ is ambiguous; the Irish Sea occurs in HRB viii.14; the English Channel is mentioned in HRB v.12.
The first name is identified by reference to the story of Beli who built a road from Kernyw to Mor Caitnes in the north. In Geoffrey of Monmouth (HRB iii.5), Belinus builds a north to south road ‘from the Cornish Sea to the shore of Caithness’ and a west to east route from ‘St David’s on the Demetian Sea to Southampton’. Blake and Lloyd identify the first road with the Sarn Elen, which they state runs from Pennal near Machynlleth to the Conwy Valley. This is a simplification of a very complex situation. Sarn Elen is the name of a group of roads associated in Welsh folklore with Elen, mother of the Custennin Fawr, in the Brut and Helena, mother of Constantine the Great, in Geoffrey of Monmouth (HRB v.6). The first record of the story is in Breuddwyd Maxen Wledig (‘The Dream of Macsen Wledig’), in which Elen Lluyddog (‘of the hosts’), wife of Macsen Wledig, builds numerous roads, all of which are said to have borne her name. In addition to being applied to the section of roads mentioned by Blake and Lloyd, it continues south from Pennal to Carmarthen via Aberystwyth and Lampeter, as well as south-east from Dolgellau along the A470 to Caersŵs at Y Drenewydd (Newtown, Powys), while a section of road in Brecon is also known by this name. In fact, no Roman road had so far been discovered leading north from Pennal, although that to the south is known; even so, it is likely that one awaits discovery. In fact, they are not entirely consistent, as Map 10, later on in the book, shows Sarn Elen connecting Caer Fyrddin (Carmarthen) with Caernarfon and Chester. To follow their logic would mean relocating ‘the Cornish Sea’ and thereby Kernyw in South Wales, something even they are not prepared to do.
What Blake and Lloyd have done is conflate two stories – that of the north to south road of Bran/Brennius and that of the numerous roads called Sarn Elen – and then use their conflated version to identify the location of the road ‘to the shore of Caithness’ with one of the Sarnau Elen. This is hardly admissible. They even stretch their definition of Kernyw southwards as far as Machynlleth to make the details fit their revised geography, despite an earlier statement that it was the Lleyn Peninsula. There is intellectual dishonesty in this chain of supposition. Nevertheless, they feel confident in asserting that Mor Caitnes was ‘off the coast of North Wales’ (in other words, Liverpool Bay).
Blake and Lloyd then use the name Σετηία ’έισχυσις (with a variant Σεγηία ’έισχυσις) from Ptolemy’s Geography ii.3, 2 as confirmation of their identification of Mor Caitnes with Liverpool Bay. They take Ptolemy’s name to refer to the Dee Estuary (it is almost certainly the Mersey, but this is unimportant to their argument) and suggest that Caitnes might be a variant of Seteia. The linguistic problems are enormous. Ptolemy’s name is best analysed as containing Brittonic *sego-, ‘power, force’ (surviving as Welsh hy, ‘daring’) with a derivational suffix *-eia, which would give a Brittonic *Segeia as the name of the Mersey. On the other hand, Caitnes contains the Old Norse nes, ‘headland, promontory’, whilst the first element is more likely to be of Celtic origin. The placename Caithness (which is the traditional identification of the name) contains Gaelic cat or cait, ‘cat’, which is thought to be a tribal name; the name is first recorded c 970 as Kathenessia.
There is no debate about the location of Mor Iwerddon, as Iwerddon is the Welsh name for Ireland, which, thankfully, Blake and Lloyd do not attempt to relocate.
Without justifying arguments or evidence, they use all of one sentence to assert that ‘Mor Ud is the original name for the Severn estuary and the Bristol Channel, the area of sea between South Wales and the southwest peninsula of Devon and Cornwall’. What is their evidence for this? The Middle Welsh word ud (or udd, sometimes spelt uđ by modern scholars) means ‘Lord’, but is hard to see how this can have been used to refer either to the English Channel or the Bristol Channel. The spelling displays a sound change (from iud to uđ) that is dated to the second half of the tenth century, so the name recorded in the Brut cannot be earlier than this (conventional scholarship places the text in the late twelfth century, anyway).