After Glyndŵr gained early successes in 1400, King Henry led a punitive expedition into north Wales and appeared to have suppressed the revolt.

[1] However, Glyndŵr remained at large, and anti-Welsh legislation by Parliament ensured that few Welshmen had reason to support continued English rule.

Early in 1402, Glyndŵr's men ambushed and captured Grey of Ruthyn, who had indirectly caused the rebellion, and held him for ransom.

In June, Glyndŵr himself was near Knighton, and only 12 miles (19 km) from Leominster, then an important English garrison and market town in the Welsh Marches.

In any case, as a substantial holder of lands in Wales and on the borders, Mortimer had already suffered from the depredations of Glyndŵr's rebels and appeared to have much to lose should the revolt continue.

[6] It was claimed by contemporary accounts that immediately after the battle, many English corpses were mutilated by Welsh women camp followers,[7] in revenge for the punitive expeditions by Henry IV in the previous years, which had been marked by many acts of brutality and rape.

Whether these mutilations took place remains open to debate, as some historians, including Philip Warner, suggest it was a story perpetrated by the English parliament to portray the Welsh as savages.

Mortimer subsequently renounced his allegiance to King Henry IV, put forward his nephew's claim to the throne of England, and married Glyndŵr's daughter Catrin.

The battle is mentioned by William Shakespeare in Henry IV, Part 1: the noble Mortimer, Leading the men of Herefordshire to fight, Against the wild and irregular Glendower, Was by the rude hand of that Welshman taken,

A thousand of his people butcheredThe Welsh Battlefields Survey carried out by the Royal Commission on the Ancient and Historical Monuments of Wales (RCAHMW) said that it is not possible to identify the exact location of the battle from the available documentary and archaeological evidence.

A computer-animated reconstruction of the battle was featured in the BBC series, Battlefield Britain, narrated by Peter Snow.

[11] The battle is described in Chapter XV, entitled 'Bryn Glas', of John Cowper Powys's historical novel Owen Glendower (1941).