Battle of Bryn Glas The Battle of Bryn Glas , ( sometimes referred to in English accounts as the Battle of Pilleth - although Bryn Glas translates as green or blue hill ) was fought on 22 June 1402 , near the towns of Knighton and Presteigne in Powys . It was a great victory for the Welsh rebels under Owain Glyndŵr , and it resulted in the prolongation of the Welsh rebellion and the destabilisation of English politics for several years afterwards . Background . Owain Glyndŵr ' s revolt occurred against a background of instability in the English monarchy . King Richard II of England had become alienated from many of the nobles , and had been overthrown by Henry Bolingbroke , the Duke of Lancaster , who became Henry IV of England . In Wales and the Welsh Marches , there were still many supporters of the deposed Richard , who died in captivity in 1400 . In that year , Reginald Grey , 3rd Baron Grey de Ruthyn , a supporter of the new King Henry , had unlawfully seized some of Glyndwr ' s lands and falsely caused charges of treason to be brought against him . In response , Glyndwr declared himself the true Prince of Wales , and began a rebellion . After Glyndwr gained early successes in 1400 , King Henry led a punitive expedition into North Wales and appeared to have suppressed the revolt . However , Glyndwr remained at large , and anti - Welsh legislation by Parliament ensured that few Welshmen had reason to support continued English rule . On 1 April 1401 ( which was Good Friday ) , two brothers from Anglesey , Rhys ap Tudur and Gwilym ap Tudur , seized Conwy Castle by trickery . Glyndwr himself won a victory over an army of English and Flemish settlers in Pembrokeshire at Mynydd Hyddgen in mid - Wales . These two events reinvigorated the rebellion . Henry led another punitive expedition into mid - Wales , but achieved nothing and his army suffered severely from bad weather . Early in 1402 , Glyndwr ' s men ambushed and captured Grey of Ruthin , who had indirectly caused the rebellion , and held him for ransom . In June , Glyndwr himself was near Knighton , and only from Leominster , then an important English garrison and market town in the Welsh Marches . King Henry had appointed Henry Percy , widely known as " Hotspur " , as his principal lieutenant and justiciar in North Wales and the adjacent Marches . Hotspur ' s uncle , the Earl of Worcester , held a similar appointment in the south . However , the force which confronted Glyndwr near Knighton was a county levy of Herefordshire under Sir Edmund Mortimer . Mortimer was uncle of the young Edmund de Mortimer , 5th Earl of March , and either of them had a better hereditary claim to be King of England than Henry . ( The childless Richard II had declared Sir Edmund ' s brother and the young Edmund ' s father , Roger Mortimer , 4th Earl of March to be heir apparent to the crown , but Roger had died the year before Richard was overthrown and none of the nobles supported his son ' s claim . ) However , Sir Edmund Mortimer had so far loyally supported the new king . 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 . Battle . There were few contemporary sources for details of the battle , and some , such as that of Adam of Usk , contained inaccuracies . Most details must therefore be assumptions , although the ground remains largely unchanged and provides a reasonable basis for them . Mortimer ' s army was seeking to bring Glyndŵr ' s smaller army to battle . Although the location was only just inside Wales , Glyndŵr undoubtedly had many local informants and sympathisers , and could plan a decisive battle . Probably , he had also been able to summon reinforcements from other parts of Wales , which moved rapidly over hill tracks , and was therefore far stronger than Mortimer realised . Though always a risky tactic , Glyndwr divided his army . Part of the army , including many archers armed with the powerful longbow , was placed on the slopes of the hill . The remainder were concealed in a valley to the left of the hill , camouflaged by thick foliage . Mortimer ' s army formed up and advanced up the slope , against the Welsh archers clearly in view . With the advantage of height , Glyndwr ' s archers outranged Mortimer ' s ( themselves armed with longbows ) . As Mortimer ' s men at arms tried to close with Glyndwr ' s archers , the Welsh troops who had been concealed in the valley emerged to attack Mortimer ' s right flank and rear . At some stage , contingents of Welsh archers in Mortimer ' s army defected , and loosed arrows against their former comrades . It is not known whether their defection was planned in advance , or whether they chose to back Glyndwr in the middle of the battle as the likely winner . Their action contributed to the confusion of Mortimer ' s army which , attacked from the steep slopes above , and from their flank and rear , was destroyed . Among those killed were Sir Walter Devereaux of Weobley , and Sir Robert Whitney , who was Henry IV ' s Knight - Marshal . Aftermath . It was claimed by contemporary accounts that immediately after the battle , many English corpses were mutilated by Welsh women camp followers , in revenge for the punitive expedition s 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 . The English dead lay unburied , and the stench caused the area to be avoided for months . The battle was one of the greatest Welsh victories against an English army in the open field . News of it brought many Welshmen who had hitherto been undecided to openly support Glyndwr . On the English side , it resulted in some panicked appointments of officers and hasty reinforcements of garrisons all over Wales . Mortimer was captured in the battle . Henry ( who was in financial difficulties ) made no effort to ransom him . 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 Caitrin . The battle is mentioned by William Shakespeare in Henry IV , Part 1 : The contemporary site . A church at Pilleth that predates the battle and a stand of Wellingtonia planted to commemorate it , mark the actual site of the battle . There is limited parking at the recently renovated church . In the grounds of St Mary ' s Church is a spring - fed well ; testament to ancient celtic connections . Reconstructions . A computer - animated reconstruction of the battle was featured in the British Broadcasting series , " Battlefield Britain " , narrated by Peter Snow .