Einion the second son of Rhys ap Hywel, whose attainder has been noticed, embraced a military life and served our third Edward in the memorable battles of Cressy and Poictiers; after a long residence in England he returned to his
native country with considerable opulence and married the rich heiress of Howel, lord of Miscin in Glamorganshire; he became possessed by purchase of nearly the whole of what is now called the hundred of Devynnock, from Llywel on the borders of Carmarthenshire to the river Tarell near Brecon. He built a castellated mansion for his residence in the parish of Llandspyddid, lately called the castle field, now the property of Penry Williams of Penpont, esquire: it is described to have been sitmacted on the fall of a small brook into the Usk, near Bettws or Penpont chapel: there is still an unevenness in the surface of the ground, though there are not now the smallest vestiges of buildings remaining; Hugh Thomas, who wrote in 1698, recollects to have seen the ruins, and there are others living who remember the rubbish being removed and the soil cleared of the stones and materials of the walls: it was called from the owner, Castell Einion Sais, or Einion the castle, an appellation by which the Welsh to this day sometimes distinguish not only the English settlers among them, but also their own countrymen who have been brought up and educated in England. -- probably from History of the County of Brecknock by Theophilus Jones (1898), volume 2: page 80.1
Occasionally the most barbaric insolence and atrocity were practised towards them. Thus we find that the tyrannic William de Breos brutally murdered Trahaern Fchan, Lord of Llangorse, [this seems to be Trahaern ap Gwgan] a grandson of Bleddyn ap Maenarch. Having a spite against him for some cause unknown, he treacherously invited Trahaern to meet him for consultation on a matter of business. The Welshman unsuspectingly went unarmed, was met on the road not far from Brechnock by the cruel oppressor, seized without ceremony, tied to the tail of a horse, and dragged through the streets of the town to a place of execution, beheaded, and his body suspended for three days on a gibbet. The will of the Lord Marcher was law, and where the man happened to be a monster, as in this case he was, the subject Welsh were frequently miserable sufferers. The tyrant followed the 'simple plan,' - 'That they should take who had the power.'
possible source: Ancestors of Evelyn Wood Keeler; Josephine C Frost (1939}
Cites as references for Welsh lineages: Royal Families of England, Scotland, Wales: Volume I & 2; Genealogical Tables of the Sovereigns of the World; Maunder's Biographical Treasures; Universial Biography; etc.1
Giraldus Cambrensis refers, in too mild a way, to another, and if possible a more atrocious instance of William de Breos's cruelty, which occurred not at Brecknock, but at Abergavenny. His uncle Henry, of Hereford, having been murdered in A D 1176, William invited a large number of Welsh into the Castle of Abergavenny, under pretest of holding a conference with them; but having got them together as guests, he proposed that they should take an oath 'that no traveller by the waie amongst them should beare any bow, or other unlawful weapon,' as Hollingshed expresses it. Having refused to take such an oath, they were told they must atone for the refusal by death. He called his men-at-arms, and slaughtered them to a man. Giraldus speaks of this massacre as among 'the vindictive retaliations of the governors against the natives; ' but he half excuses De Breos, as being only driven to such excesses by Henry II.
source: Annals and Antiquities of the Counties and County Families of Wales; Dr Thomas Nicholas {1875}: Page: I:85, 118.1