This important battle is briefly mentioned in many English chronicles (Latimer), but it is the Brutiau that provide the best evidence for its location. Henry II brought a massive army to Oswestry while the Welsh rulers, Owain Gwynedd and his brother Cadwaladr, The Lord Rhys of Deheubarth and Owain Cyfeiliog and Iorwerth Goch of Powys, in a rare moment of unity, gathered their forces at Corwen:

'A gwedy trygyaw ynn hir yn y pebylleu yno hep arueidaw o un gyrchu y gilyd y ymlad, llidyaw a oruc y brenhin yn diruawr; a chyffroi y lu hyt yg koet Dyffryn Keiriawc, a pheri torri y coet a?e uurw y'r llawr. Ac yno yd ymerbynnyawd ac ef ynn wrawl ychydic o Gymry etholedigyon, y rei ny wydynt odef y goruot, ynn abssenn y tywyssogyon. A llawer o rei kadarnnaf a dygwydawd o bop tu. Ac yna y pebyllawd y brenhin, a'r bydinoed blaen y gyt ac ef, ymynyded Berwyn. Ac gwedy trigyaw yno ychydic o dydyeu, y kywarsagwyt ef o diruawr dymestyl awyr a thra llifeireint glawogyd. A gwedy pallu ymborth idaw yd ymhoelawd y bebylleu a?e lu y uaestir gwastatir Lloegyr' (Jones, 1955, 145-7)

Translation: 'And after staying long in their tents there without the one daring to attack the other, the king was greatly angered; and he moved his host into the wood of Dyffryn Ceiriog, and had the wood cut down and felled to the ground. And there a few picked Welshmen, who knew not how to suffer defeat, manfully encountered him in the absence of their leaders. And many of the doughtiest fell on both sides. And then the king, and the advanced forces along with him, encamped on the Berwyn Mountains. And after he had stayed there a few days, he was oppressed by a mighty tempest of wind and exceeding great torrents of rain. And when provisions had failed him, he withdrew his tents and his host to the open lands of the flats of England' (Jones, 1955,145-7).

The English sources refer to the event as taking place in the Berwyn mountains, but none of them supply the more specific Coed Ceiriog, which is also the name used in the Gwynedd chronicle O Oes Gwrtheryn (Jones, 2013, 418). Humphrey Lhwyd in his Cronica Walliae (1559) elaborates the account slightly, but David Powel, using Lhwyd's text as a basis for his printed work, is the source of some confusion about this event (Powel, 221-2). The `picked Welshmen? of the Brutiau become the `piked men? of Henry's army and he also inserts a passage, from Holinshed's Chronicle (1577), about Henry II coming under attack and being saved by Hubert de St Clare (Powel, 222). This passage originates from the chronicle of Ralph Niger and refers to events at Bridgnorth, not the Ceiriog valley.

The earliest author to refer to this event as the battle of Crogen was Thomas Pennant in 1778:

'This conflict is sometimes called the battle of Corwen; but with more propriety that of Crogen: for it happened beneath Castell Crogen, the present Chirk Castle; and the place is still called Adwy'r Beddau, or the pass of the graves of the men who were slain here' (Pennant, vol 1, 268).

This relies on his identification of Chirk castle as Castell Crogen which is not supported by medieval documents (Carr, 190); they place it at the motte at Crogen, in Llandderfel, near Bala (SJ 0060 3699). The existence of Crogen placenames in the vicinity of Chirk Castle probably led to Pennant's assumption. Following Pennant, Crogen has become widely accepted as the name of the battle and a commemorative plaque to the event has been installed on Castle Mill Bridge near Chirk (SJ 2637 3757; NPRN 310228).

The available evidence locates the site somewhere in the Ceiriog valley, between Chirk and Llanarmon Dyffyrn Ceiriog, but is not sufficient to be any more exact.

RCAHMW, Jan 2017

Bibliography
Carr, A.D.,?The Barons of Edeyrnion 1282-1485?, Journal of the Merioneth Historical and Record Society, 4/3 (1963), 187-93.
Jones, Owain Wyn, `Historical writing in medieval Wales? (Bangor University, PhD thesis, 2013).
Jones, Thomas (ed. and trans), Brut y Tywysogyon or the Chronicle of the Princes: Red Book of Hergest Version (Cardiff, University of Wales Press, 1955).
Latimer, Paul, `Henry II's campaign against the Welsh in 1165?, Welsh History Review, 14/4 (1989), 523-44.
Pennant, Thomas, A Tour in Wales MDCCLXXIII (London, 1778).
Powel, David, The Historie of Cambria, now called Wales (London, 1584).
Williams, Ieuan M. (ed.), Humphrey Llwyd Cronica Walliae (Cardiff, University of Wales Press, 2002).