The Diocese of Glasbury (Welsh:) was founded in The Bishops of Glasbury are listed in a 14th-century manuscript. A less reliable list of bishops was recorded by the chronicler-monk Geraldus Cambrensis (Gerald of Wales). Situated approximately 15km (09miles) northeast of Llangors, it was the site of an early Christian church from at least the 950s, it may have become a suffragan diocese of St Davids. At least in its early years, the diocese appears to have enjoyed the support of the kings of Brycheiniog, and this enabled Glasbury's bishops to compete with their rivals at Ergyng, such as Euddogwy.
| Brecchert | |||
| Cynidr | |||
| Gwyfan [?Gwrfan] | |||
| Gwrfryd | |||
| Meilyg | |||
| Morgynnydd | Mid-10th century | Or Morgennic. Mentioned by Gerald as Morgeneu. May have succeeded Rhydderech. | |
| Rhydderch | 955 | Mentioned by Gerald, but placed too early in his list. May have predeceased Morgynnydd. | |
| David | |||
| Wilfred | |||
| Ithel | |||
| Erwyd [?Erfyn] | 1040 | Also recorded as Heruit, itself a misspelling of Heruin. | |
| Ælfric | |||
| Tryferyn | Diocese amalgamated with the Diocese of Hereford. Possibly to be identified with Tramerin, also mentioned by Gerald. Known to John of Worcester for his piety. Tryferyn appears to have deputized in Hereford for Bishop Æthelstan, who went blind. |