There are various interpretations given to the word "Clyro". It is thought to mean "shining" or "clear water". The old names were "Cleirwy" and "Clidderwy", meaning "The Wye flowing on a bed of clay".
Evidence of ancient habitation is given by local finds of prehistoric flint arrowheads and a stone axe head. Clyro Hill Tump may be the site of a round barrow or a motte. An unexcavated mound elsewhere may be a long barrow. At Clyro Court Farm there is a prehistoric chambered tomb made of upright slabs. The Romans built a fort in Clyro nearer the river by what is now Boatside Farm. This suggests the use of the area as a means of communication between east and west. But later Offa's Dyke was constructed just by Clyro, thus creating a boundary between countries. Later drovers' roads served the purpose of getting livestock from Wales to England and London. Earthworks remain of Clyro Castle but the stone fabric has gone. Its erection also seems to testify to the importance of Clyro as the stage along a journey.
Although the present church is mostly of nineteenth century construction, this was a rebuilding of an earlier mediaeval church. A look at a map even as late as the 1880's shows the pattern of a typical self-supporting, mediaeval village, with habitations grouped around the church: a stream flowing by it that services a mill. There were probably earlier mills along the stream as some names and some ruins suggest. There was a succession of smithies. Within Clyro Court Farm are the remains of a monastic grange, probably founded from the Cistercian abbey of Cwmhir. There is part of a stone barn and a fourteenth century arch.
It is thought that the castle at Clyro had some defensive link with Hay-on-Wye Castle. Just to the north-east of the village is another site of fortification at Court Evan Gwynne. Paul Remfry in his Castles of Radnorshire considers that Clyro Castle was probably built in the 1070's. It was perhaps destroyed in the 1140's and rebuilt in the thirteenth century, being still defensible in 1403. The stone castle was built on the top of the mound, and the whole site was enclosed by a polygonal curtain wall. To the south was probably a gatehouse or keep. What remain now are earthworks covered by mature trees.
The life of the village progressed unrecorded for centuries. In 1801 the whole estate of Clyro was inherited by an Oxford don, the Reverend Doctor William Powell, who built the large Regency style house "Cae Mawr". Later the whole estate was sold to the Baskerville family who built Clyro Court in 1839. The coat of arms of the Baskerville family has the head of a hound pierced by a shaft. Although Sir Arthur Conan Doyle set his story The Hound of the Baskervilles in the West Country, it is believed that his visit to Clyro gave him some of the source material.
The daily life of Clyro has been evocatively preserved in the diaries of the Reverend Francis Kilvert, curate here in the 1860's and 70's, while he lodged at Ashbrook House, now a
contemporary art gallery that also incorporates his memory. A hundred years after Kilvert lived here Laurence Le Quesne recorded the life of the village, published as After Kilvert by Oxford University Press. The Baskerville Estate was sold off in the 1950's. The coming of the railway to Hay-on-Wye may have brought about some change in the appearance and way of life in Clyro, but on the whole the radical changes happened after the demise of the Baskerville Estate. The whole area had been a place of woods and extensive orchards as celebrated by Kilvert. In more recent times the A438 cut a swathe to one side of the village and opened up a greater mobility and all that comes with it. The break-up of estates often means the visual fragmentation of a settlement. Unless the resulting vacuum is filled by an authority conscious of design, exploitation results. The Castle Estate was built up against the castle mound; Begwyns Bluff Estate was developed on a hill above the village and Baskerville Court Estate was built on a slope behind the nineteenth century "Baskerville Arms".