949: "King Hywel the Good died . . . then the battle of Carno took place between the sons of Hywel and the sons of Idwal." Source: Thomas Jones, The Chronicle of the Princes, 1955, p.13.
949 or 950: The men of Gwynedd marched to meet the sons of the dead king [Hywel Dda] under the leadership of their own princes, Iago or Jacob and Idwal or Ieuaf, the sons of Idwal the Bald. The battle was fought at Nant Carno, in the region of Arwystli, on the border of North and South Wales, and was a victory for the sons of Idwal.
Source: J.E.Lloyd, A History of Wales, vol I, 1912, p.344.
"It is well known that these mountains of Carno were the scenes of the bloody battles fought some time after the death of Hywel Dda, A.D. 949. The contending parties were the men of North Wales, led on by Ieuaf and Iago, sons of Idwal Foel, on the one hand, and the men of South Wales, by Owen Rhun, Roderic and Edwin, their cousins, when the Northwallians became masters of the field." Source: Archaeologia Cambrensis, III, 3rd series, 1857, p.302.
"Twr Gwyn Mawr. Welsh historians and antiquaries of two or three generations ago were wont to associate the carneddau on the high land between the parishes of Carno and Llanbrynmair, and especially the carnedd known as Twr Gwyn Mawr [nprn 304912], with the conflicts mentioned in the Welsh chronicle called Brut y Tywysogion under the years 948 and 1080 [nprn 405052] A.D." Source: RCAHMW Montgomeryshire Inventory, 1911, no.43.
The site is marked on early Ordnance Survey maps as "Twr Gwyn (Cairn) (Supposed site of Battle A.D.948)" B.A.Malaws, RCAHMW, 17 OCtober 2006.