It is considered the first victory in the field won by Owain Glyndŵr (1359–c. 1416), leader of the Welsh revolt and it could be said that it set the tone for the spread of the rebellion in its early stages and at a key time if the rebellion was to gather meaningful momentum.
The battle began when English settlers of Pembrokeshire and settlers of Flemish descent, (who had also settled in Pembrokeshire, encouraged by the earlier English King Henry I of England), attacked the small army of Glyndŵr, which was encamped at the bottom of the Hyddgen Valley.
The settlers were reinforced by a large force of English soldiers and Flemish mercenaries. This was Owain's early base as his rebellion started and spread. It is estimated that his force at this stage amounted to five hundred men, just a third of the attacking force and some records, such as the 'Annals of Owen Glyn Dwr' written by Gruffydd Hiraethog many years later in 1550 and based on earlier accounts that dont survive, put his force at just 120 men.
The precise location of the battle is not known, and little is known of the course of the battle itself. Mynydd means "mountain" in Welsh.
However, it is known that Glyndŵr's army was able to fight back these attackers, killing 200, chasing the main force away and making prisoners of the rest.
The Annals of Owen Glyn Dwr record that "Owen now won great fame, and a great number of youths and fighting men from every part of Wales rose and joined him, until he had a great host at his back."
The slain were buried at Bryn y Beddau, the 'Hill of Graves' nearby.