Site of a battle 'in the reign of William Rufus [1087-1100], which is said to have taken place on Hirwaun Common, about 2 miles north of the village [?Aberdare] between the forces of Rhys ap Tewdr, prince of South Wales, and those of Iestyn ab Gwrgan, aided by a body of Norman adventurers under the command of Robert Fitz-Hamon.'
(ref: Lewis, Topographical Dictionary of Wales (1849) p.7)
The battle is almost certainly fictitious. It is based on the passage in the 'Genealogy of the Kings of Glamorgan.'
(ref: Iolo manuscript (1848) 377-8 (E Williams))
The author was 'an accomplished manufacturer of bogus antiquities.'
(ref: Proceedings of the British Academy, 14 (1928) 377 (J.E.Lloyd))
Lloyd refers to the passage and says: 'in spite of the labourious peculiarity with which tradition tells the story of Iestyn's defeat and over throw it still remains a subject upon which history is perforce silent'.
(ref: J.E.Lloyd, History of Wales (1954) 402)
Source: Ordnance Survey NAR, SN90NW 10.
B.A.Malaws, RCAHMW, 02 November 2010.