To inform the consideration of The Inventory of Historic Battlefields in Wales , documentary and historical research was commissioned on the 1170 battle of Pentraeth and the resulting research report provides a detailed overview (Gildas Research).

Following the death of Owain Gwynedd in 1170, a bitter struggle broke out between his sons over who would inherit the right to rule the kingdom of Gwynedd. The first action on this long-running conflict was the battle at Pentraeth on Anglesey where Hywel ab Owain Gwynedd, the likely nominated heir, was killed alongside his six foster-brothers, by his half-brother Dafydd ab Owain Gwynedd. The event is noted in the Breviate Chronicle:

'Owinus rex Norwallie et catwaladrus frater suus minor 'scilicet hoelus filius owini a familaribus fratris sui dauid eodem assistente occisus est' (Gough-Cooper, b1193.3).

Translation: 'King Owain of North Wales and Cadwaladr his younger brother (died), certainly Hywel ab Owain was killed by the war band of his brother David, who himself stood nearby' (Remfry, 183).

Additional details including the location of the battle are provided in two contemporary poems, Marwnad Hywel ab Owain (Elegy for Hywel ab Owain) and Marwnad Meibion Cedifor (Elegy for the sons of Cedifor) written by a survivor of the battle, Hywel's foster brother Peryf ab Cedifor. In addition to a location in the parish of Pentraeth on Anglesey, three lines in the poems provide further topographical clues:

'Yn y Penrhyn uch Penrhos' (Marwnad Hywel ab Owain, line 6)
Translation: 'On the headland above Penrhos' (Elegy for Hywel ab Owain, line 6)

'Llas gwr mirain uch morfa' (Marwnad Hywel ab Owain, line 16)
Translation: 'Slain was the handsome hero, above the sea-marsh' (Elegy for Hywel ab Owain, line 16)

'Yn y pant uch Pentraeth' (Marwnad Meibion Cedifor, line 14).
Translation: In the hollow above Pentraeth (Elegy for the sons of Cedifor, line 14).

From this it has been possible to narrow down the location of the battle to a small area in the parish of Pentraeth, specifically the area surrounding a now demolished house named Pen Rhos on the first edition one inch to the mile Ordnance Survey map of 1840 at SH 526 772.

In 1996 a monument to commemorate the battle was erected on the bank of the river Nodwydd as it enters the sea in Red Wharf Bay (SH 5346 7982; NPRN 421827).

RCAHMW (Battlefields Inventory), Jan 2017

Bibliography
Gildas Research, The Battle of Pentraeth 1170: Historical Assessment (2013).
Gwaith Llywelyn Fardd i ac Eraill o Feirdd Y Ddeuddegfed Ganrif: Cyfres Beirdd y Tywysogion 2 (Cardiff, 1994).
Gough-Cooper, Henry (ed.) The Breviate Chronicle: Annales Cambriae, The B Text from London, National Archives, MS E164/1, pp. 2?26, online edition.
Remfry, Paul M. Annales Cambriae: A Translation of Harleian 3859: PRO E. 164/1: Cottonian Domitian, A1: Exeter Cathedral Library MS.3514 and MS Exchequer DB Neath, PRO E. 164/1 (Castle Studies Research, 2007).
Williams, Ifor, `Marwnad Hywel ab Owain Gwynedd? Transactions of the Anglesey Antiquarian Society (1923), 49?58.