To inform the consideration of The Inventory of Historic Battlefields in Wales , documentary and historical research was commissioned on the 1282 battle of Irfon Bridge and the resulting research report provides a detailed overview (Chapman).

The battle of Irfon Bridge between the forces of Llywelyn ap Gruffudd, prince of Gwynedd and Edward I forces near Builth was a decisive engagement determining the direction of the history of medieval Wales. Its importance comes from the fact that at the end of the battle, Llywelyn was dead and with it the possibility, at that date, of an independent Wales. Thus the event appears in nearly all the contemporary Welsh and Latin chronicles as well as correspondence between the king, royal officials and churchmen. These accounts do however conflict and thus there is no clear narrative of the event.

In November 1282, following Edward I military successes in North Wales, Llywelyn in an attempt to open up new fronts led his army out of Snowdonia and into the central Marches and then to Builth. The Peniarth MS.20 version of the Brut y Tywysogyon then notes:

'Ac efo ago refgynaud hyt en llangaenten ac odena ef a anvonef y wyr ay diftein y gymmryd gwsogaeth gwyr bsecheinyauc ac a daw y tywiffauc a bychy dic o wyr gyd ac ef. ac e na y doeth Roffer mosty myr a Grufud ap gwen nwynwyn a llu er bsehyn gantwynt en direbud am ev penn ac ena y llas llywelyn ay osevgwyr. dyw damafius bap pethew nos os vn dyd kyn dyw Nadolic a dyw gwener oed y dyd hvnnw' (Jones, 228).

Translation: 'And he gained possession as far as Llanganten. And thereupon he sent his men and his steward to receive the homage of the men of Brycheiniog, and the prince was left with but a few men with him. And then Roger Mortimer and Guffudd ap Gwenwynwyn, and with them the king's host, came upon them without warning; and then Llywelyn and his foremost men were slain on the day of Damasus the Pope, a fortnight to a day from Christmas day; and that day was a Friday' [11 December] (Jones, 120-121).

The general location of the battle, somewhere in the vicinity and lordship of Builth, is generally accepted as accurate. Only Walter of Guisborough provides a definite location although his account must be treated with a certain amount of circumspection, owing to the similarity with the same author's treatment of the battle of Stirling Bridge in 1297:

Translation: '?a Welshman pointed out to the English a ford, by which some of them crossed the Irfon and proceeded to secure Orewin bridge from the rear. The whole [English] army then crossed, and ascended to the heights beyond. The Welsh, taken by surprise, and having no orders in the absence of their prince, stood their ground manfully, and shot down upon the English, but shaken by the archers who were interlaced with the heavy cavalry, then attacked in the rear by some of the cavalry who worked round and pushed higher up the slope behind them, they broke and fled' (Smith).

A monument at Cilmery SO 00090 51407 (NPRN 32562), traditionally marks the spot of the death of Llywelyn, as indicated on historic Ordnance Survey mapping. The majority of evidence suggests this was away from the main battle; however it is not nearly precise enough to sustain or to contradict this site.

RCAHMW (Battlefields Inventory), Jan 2017

Bibliography
Chapman, A., Irfon Bridge 11 December 1282: Documentary and Historical Research Report (2013).
Jones, Thomas (gol.), Brut y Tywysogyon: Peniarth MS. 20 (Caerdydd, Gwasg Prifysgol, Cymru, 1941).
Jones, Thomas (trans.), Brut y Tywysogyon or The Chronicle of the Princes Peniarth MS. 20 Version (Cardiff, University of Wales Press, 1952).
Smith, Ll. Beverley, `The Death of Llywelyn ap Gruffudd. The Narratives Reconsidered?, Welsh History Review/Cylchgrawn Hanes Cymru, (1982-3), 200-14.