It’s a temenos, a holy grove, surrounding Pilleth’s old and simple church. It lies along a track off the road between Knighton and Presteigne near the England-Wales border, looking down from a site of no great elevation, but of seclusion and quiet beauty, on to the valley of the River Lugg. I visited here last week. Swallows and house martins still hawked around in pursuit of sparse insect fare, feeding up before long southwards migration. Swifts had left weeks before. I first came to this lovely place 40 years ago. The little church, St Mary’s, with its sturdy bell tower, then had something of a ramshackle, neglected air. My late son Will was with me. I told him the story of Owain Glyndŵr’s great uprising against English rule at the outset of the 15th century. It was here at Pilleth, on 22 June 1402, that he fought a major battle against the English force of Edmund Mortimer. As with the battle at Hyddgen the previous year, ground advantage was to the Welsh: Glyndŵr’s warriors had established themselves on the steep ridge of Bryn Glas above the church. The English stumbled up the steep hill; Glyndŵr’s men fell upon them. The Welsh longbowmen in the English force suddenly changed sides and allied with Glyndŵr. Mortimer’s soldiers were slaughtered, he was taken prisoner and married off to a daughter of Glyndŵr. It was the actions of the Welsh female camp-followers after the battle that struck a crucial psychological blow. They cut off the genitals of the English dead and left them lolling from their mouths. The story was widely circulated by medieval chroniclers, and instilled dread. Twenty years ago on a window ledge within the whitewashed church were spurs, a sword, a cuirass. They were not from the battle, but had belonged to Siôn ap Rhys, MP for Brecon in the early 16th century. Within the last 20 years they’ve been stolen. I walk outside and stand by a marked mass grave in the churchyard. A barn owl ghosts by, tail of some small rodent trailing from its talons. Jackdaws are clamorous from the nearby copse of Wellingtonia that marks another mass grave. Pipistrelles jag past. Silence and darkness are gathering as I leave. Country diary is on Twitter at @gdncountrydiary