According to the 'Chronicon ex Chronicis' (Chronicle of Chronicles) of John of Worcester, written 1135-40, a battle took place in Gower on 01 January 1136..

"Immediately after the death of King Henry, on 2nd December, a fierce battle took place on 1st January in Gower between the Normans and the Welsh in which five hundred and sixteen of both armies died. Their bodies were horribly scattered among the fields and eaten up by wolves."
A similar note concerning the battle is found in the 'Gesta Stephani' (Deeds of King Stephen) written before 1148. Gerald of Wales narrows down the probable location of the battle in his 'Itinerarium Cambriae' (Journey Through Wales), written in 1191, when he notes the following on his journey from Swansea to Kidwelly.

"Next we made our way through the open countryside towards the river Loughor. Not long after the death of Henry I, Hywel ap Maredudd from Brecknockshire fought a pitched battle here against the local English, killing quite a few of their regular troops."
This suggests that the most likely site for the battle is in an area centred upon Carn Goch Common, although a definite location is not possible. The battle occured very soon after the death of Henry I and was a notable defeat for the Normans in South Wales. The figure of 516 for the number of soldiers killed is very precise and attests to teh ferocity of the battle. Gerald of Wales names the leader of the Welsh contingent as Hywel ap Maredudd ap Rhydderch, who controlled Cantref Bychan and Ystrad Tywi at the time of the battle.

A detailed discussion of the documentary sources for the battle was compiled by Gildas Research in 2013.

A memorial stone (NPRN 408150) was erected on Carn Goch Common and unveiled on 01 March 1986.

Sources:
Gildas Research, 'Welsh Battlefields Historical Survey: The Battle of Gower 1136, Glamorganshire, Historical Assessment' (2013)

McKurk, John, (ed. and trans.), The Chronicle of John of Worcester: Volume III: The Annals from 1067 to 1140 with the Gloucester Interpolations and the Continuation to 1141: The Annals from 1067-1140, Vol 3 (Oxford, 1998), pp. 218?9.

Potter, K. R. and Davis, R. H. C., (ed. and trans.), Gesta Stephani (Oxford, 1976), p. 15.

Thorpe, Lewis, (ed.), Gerald of Wales: The Journey Through Wales/The Description of Wales (Harmondsworth, 1978), p. 136.

S. Lloyd, RCAHMW, June 30 2014