Cantref
A cantref (derived from the welsh "Cant" meaning a hundred)was division of land in Medieval Wales, it was a unit of land made up of 100 tref, a tref was a small village or settlement, the equivalent word in England for a cantref was a hundred. Later as populations inceased, the commote 0r cymwd became the unit used for 100 tref, and the cantref became a larger unit, cantref could vary considerably in size; most were divided into two or three commotes but the largest, the "Cantref Mawr" or "Great Cantref" in Ystrad Tywi (now in Carmarthenshire) was divided into seven commotes, and the island of Anglesey was divided into three cantrefi, Cemais, Aberffraw and Rhosyr.
The early Kingdoms of Buellt and Gwrtheyrnion
Buellt was a cantref in medieval Mid Wales east of the River Wye. It seems to have developed along earlier Celtic tribal boundaries, its boundaries were rivers Wye and Tywi and north of a line drawn roughly between Erwood and Llanwrtyd as far as the Cambrian Mountains. It got its name from the Welsh words 'Bu' and 'Allt', be translated as 'The Wild Ox of the Wooded Slope'. Its capital was at Caer Beris
Unlike most cantrefs it was not part of any of the major Welsh kingdoms, and was instead ruled by an autonomous local dynasty, the first of whom was Pasgen. Pasgen was the third son of Vortigern. Though their father was deposed, Pasgen reached an agreement with the new ruler of Britain,Ambrosius Aurelianus.whereby they were able to retain the major part of their family’s lands. Pasgen was thus recognised as King Buellt and Gwerthrynion (which was named after his father).
According to folklore, Buellt is the location Carn Cabal, which was created when King Arthurs' dog Cabal stepped on a stone and marked it with his pawprint during the hunt for the divine boar Troit. Afterward, Arthur placed the stone on top of a hill, and anyone who tried to move it would find it back in place the next day. The placename survives in modern Wales as Carn Cafall near Rhayader.
Gwrtheyrnion was a cantref in medieval Mid Wales north of the River Wye. It is said to have been named after Vortigern (in Welsh Gwrtheyrn) as the place he fled to after Saint Germanius of Auxerre had castigated him for his various sins. Vortigerns', family probably stemmed from the Gloucester area, with the seat of his power probably in Cirencester. Gwrtheyrnion could have been his personal estate, acquired at the end of Roman rule, or it may have the place he moved to before or after the fall of Gloucester in 577 as a result of the British defeat at Dyrham at the hands of the West Saxons.
When Vortigern died, his son Pascent was put in charge of Gwrtheyrnion and Buellt by Ambrosius Aurelianus. Generally, its boundaries were the cantrefs of Arwystli to the north, Maelienydd to the east, Elenydd to the west, Efael to the southeast, and Buellt to the southwest, with its capital at Rhayader, (from which Radnorshire was later named). Between 406 and 760, it was ruled directly from Buellt and subject to its rule and by 800 had ceased to exist, being absorbed by Seisyllwg and then Deheubarth.
Rulers of Buellt and Gwrtheyrnion
c.406 - c.440 Pasgen ap Gwrtheyrn
c.440 - c.475 Braigad ap Pasgen Joint ruler
c.442 Morgan ap Pasgen Joint ruler
c.475 - c.510 Idnerth ap Briagad
c.510 - c.545 Meurig ap Idnerth
c.545 - c.580 Pawl ap Meurig Sub-king to Brycheiniog for a time.
c.580 - c.615 Elaed ap Eldoc ap Pawl
c.615 - c.650 Morwd ap Elaed
c.650 - c.685 Gwyddgan ap Morwd
c.685 - c.715 Pasgen Buellt
c.715 - c.745 Tedwr ap Pasgen Joint ruler
c.720 Glowd ap Pasgen Joint ruler
c.745 - ? Ffernfael ap Tewdr Last king of Buellt and Gwrtheyrnion.
c.785 Braustud ferch Glowd Daughter of Glowd, married Arthfael Hen (the Old) of Glywissing.
by 800 The kingdom ceases to exist, being absorbed by Seisyllwg and then Deheuberth.