The Bonedd y Sant (Lineages of the Saints) survives from the early 13th century in multiple copies and is believed to have been compiled in 12th century Wales. An extensive and fanciful lineage of Oswald is one of the only Anglo-Saxon entries.
“ Osswallt ap Oswydd aelwyn ap Ydolorec vrenin  Eda Glynuawr ap Gwynbei drahawc ap Mwc Mawr Drevydd ap Offa kyllellvaw, vrenin Lloeg, y gwr a ymladdodd yn erbyn Arthvr gNgwaith Vadon.” (Bartrum,1966, p. 64)
My (loose) translation:
[St.] Oswald son of Oswiu Fair (Eye-)Brow son of Æthelric the King. [son of] Ida Great Knee son of Gwynbei the Arrogant son of Mwng of Great Towns son of Ossa Great Knife, King of England, the warlike man who contended with Arthur at the battle of Badon.
(ymladd = fight/fighter; erbyn= meet)
There is a general agreement that lineages 70 and 71 are supposed to be one lineage. There is some really warped similarity to the Historia Brittonum and Anglo-Saxon Genealogies that should read like this:
Oswald and Oswiu [sons of Æthelfrith Flexor] son of Æthelric [the King] son of Ida [Great Knee] son of [rec. Eoppa] son of Ossa [Great Knife]
These epithets are strongly attached to each of these figures in Old Welsh and Cambro-Latin literature.
Considering how strong Æthelfrith Flexor was in Welsh folklore, its surprising that he is omitted from the lineages, but I believe that that he and his father Æthelric were occasionally confused. Both are mentioned several times in the Welsh triads, but its odd that Æthelric who only ruled for 4 years when Bernicia was restricted to the territory immediately near Bamburgh would be so well known.
The error in making Oswald the son of his brother Oswiu is a fairly easy scribal error from a genealogy something like the Historia Brittonum which lists brothers in the terminal generation. In Old Welsh ‘son of’ is sometimes abbreviated as “ap” from “map”, which is easy to confuse with “a” short for “and”. Bartrum notes that a late medieval poem by Cynddelw on St Tysilo that mentions the battle of Cogwy/Maserfelth and used “Osswallt vab Oswi Aelwyn”.
It appears that the author knew that some of these famous figures were part of St Oswald’s ancestry, but he also knew that with only these famous ones it was too short. With the addition of Gwynbei ap Mwc (inserted as a unit) the pedigree does get long enough to reach back to the Annals Cambriae‘s date for the battle of Badon in 516.
Over the next several weeks, I’ll be discussing the folklore of these Bernician ancestors of St Oswald from Old Welsh literature in the folklore Friday posts. Incidentally, the Bernician kings are virtually the only English figures to have specific epithets in Welsh lore, even though Edwin and Penda are also well known.
PC Bartrum, ed and trans. 1966. Early Welsh Genealogical Tracts. Cardiff: University of Wales Press.
PC Bartrum, 1993. A Welsh Classical Dictionary: People in History and Legend up to about AD 1000. National Library of Wales.