Unlike most Border parishes, Glasbury lies on both the Breconshire and Radnorshire sides of the Wye, and has in consequence been bandied about like a shuttlecock, being sometimes in Breconshire, sometimes in Radnorshire, whilst in the reign of Edward I a State Inquiry was held as to whether Glasbury lay in the county of Hereford. Indeed, in old Inquistions it frequently appears under the heading of Hereford. Williams, in his "History of Radnorshire," is probably right in describing this division of the parish "as a baronial arrangement" made by Bernard Newmarch. In the reign of Henry VIII the marches were first formed into shires, and it was then decreed that the whole of Glasbury, on both sides of the river, should henceforth be included in the country of Radnor. But though the one parish, each was to maintain its own poor, raising its own quota of militia and assessing its own rates. This arrangement continued till the year 1832, when an Act was passed for rectifying the boundaries of counties in order to facilitate the polling of the electors, and the Wye, comprising about 470 acres, was given to Breconshire. Consequently Glasbury is now both in Breconshire and Radnorshire. In the old Welsh territorial divisions, Glasbury was included in the cwmwd of Llech Ddyfnog, and the cantref of Elfael.

Much of the history of a place is often to be found in its name, and this is certainly the case with regard to Glasbury. The Duoglot composition of the name tells us that both Celt and Saxon have held sway here; and if we needed any information as to which race had been first in the field we should find it in the fact that the Celtic half of the name has the priority. Secondly, the word speaks of religion and war i.e., the Clâs or Monastery of Celtic times, and the Bury (Burh) of fort of the later Saxon invader. It is worthy of note that the Welsh name of the place, which was in use down to comparatively modern times, altogether ignores the Saxon suffix of "bury," and simply "Y Clas ar Wy," The Monastery on the Wye. And this name-lore, if we so call it, is curiously confirmed by history.

Prior to the Norman Conquest we find only two facts on record with reference to Glasbury. The earliest mention of the place is connected with a Celtic Saint, and states that St. Cynidr, a grandson of Brychan, was buried at Glasbury. He was Patron Saint of the Church there, and, considering these facts together, there seems little doubt that the Clâs was the religious establishment which he founded there, and chose as his burial-place.

The second allusion to Glasbury occurs in the year 1056, when a great battle was fought there between the Welsh and the Saxons. The Anglo-Saxon Chronicle gives the following graphic account of the battle:- "In this year [1056] died Æthelstan, the venerable Bishop [of Hereford], on the IV of the Ides of February , and his body lies at Hereford town; and Leofgar was appointed Bishop. He was Earl Harold's mass priest. He forsook his chrism and his rood, his ghostly weapons, and took to his spear and his sword after his bishophood, and so went in the force against Griffith the Welsh King, and he was slain, and his priests with him, and Ælfnoth the shire-reeve, and his many good with them, and the others fled away. This was eight days before midsummer. It is difficult to tell the distress and all the marching and camping and the traveil and destruction of men and horses which all English army endured until Leofric the Earl came thither, and Harold the Earl, and Bishop Aldred, and made a reconciliation between them.

Links to books on Glasbury

Here is a link to Maesllwch Castle  http://history.powys.org.uk/history/hay/maesmenu.html