Powys was an important early medieval Brittonic kingdom. It's mentioned by name in several sources, including the poetry attributed to Llywarch Hen and Taliesin, (legendary?) bards of the sixth or seventh century, the Historia Brittonum (written in the early ninth century according to its prologue), and an inscription on the Pillar of Eliseg, erected (according to its inscription) by a ninth century king of Powys.
The medieval Welsh territory of Powys occupied what is now east-central Wales, approximately west of Offa's Dyke and stretching from approximately Mold in the north to somewhere in the region of modern Montgomery in the south (see map on Wikipedia). What about the early medieval kingdom?
Historia Brittonum, written in the early ninth century according to its prologue, associates the founding of the kingdom of Powys with a visit to Britain by St Germanus of Auxerre and claims a continuous line of dynastic descent up to the chronicler's own time.
32. At that time St. Germanus, distinguished for his numerous virtues, came to preach in Britain: by his ministry many were saved; but many likewise died unconverted. Of the various miracles which God enabled him to perform, I shall here mention only a few: I shall first advert to that concerning an iniquitous and tyrannical king, named Bennlli.
35. The following day, the hospitable man who had been converted by the preaching of St. Germanus, was baptized, with his sons, and all the inhabitants of that part of the country; and St Germanus blessed him, saying, "a king shall not be wanting of thy seed for ever." The name of this person is Catel Drunluc: "from henceforward thou shalt be a king all the days of thy life." Thus was fulfilled the prophecy of the Psalmist: "He raiseth up the poor out of the dust, and lifteth up the needy out of the dunghill." And agreeably to the prediction of St. Germanus, from a servant he became a king: all his sons were kings, and from their offspring the whole country of Powys has been governed to this day.
--Historia Brittonum, available online
St Germanus visited Britain on two occasions, dated by Bede to 429 AD and 438 AD (Bede, Ecclesiastical History, Book I Ch. 17 and Ch. 21), and the visits are known from a hagiography written by Constantius of Lyon in 480 AD.
Whether the story of the wicked king, etc, is literally true or not, it indicates that the kingdom of Powys was considered in the ninth century to have had a long history.
The name of the wicked king, Benlli, occurs in the name of Foel Fenlli hill fort between Mold and Ruthin, which suggests that the territory of early medieval Powys included some of north-east Wales. The location is consistent with the later medieval territory of the same name.
The Pillar or Cross of Eliseg stands near Llangollen in what is now central Wales. Click on the grid reference in the Wikipedia article cited below for the precise location.
The inscription reads:
Concenn son of Catell, Catell son of Brochmail, Brochmail son of Eliseg, Eliseg son of Guoillauc.
And that Concenn, great-grandson of Eliseg, erected this stone for his great-grandfather Eliseg.
The same Eliseg, who joined together the inheritance of Powys . . . throughout nine (years?) out of the power of the Angles with his sword and with fire.
Whosoever shall read this hand-inscribed stone, let him give a blessing on the soul of Eliseg.
This is that Concenn who captured with his hand eleven hundred acres [4.5 km²] which used to belong to his kingdom of Powys . . . and which . . . . . . the mountain
[the column is broken here. One line, possibly more, lost]
. . . the monarchy . . . Maximus. . . of Britain . . . Concenn, Pascent, Maun, Annan.
Britu son of Vortigern, whom Germanus blessed, and whom Sevira bore to him, daughter of Maximus the king, who killed the king of the Romans.
Conmarch painted this writing at the request of king Concenn.
The blessing of the Lord be upon Concenn and upon his entire household, and upon the entire region of Powys until the Day of Judgement.
The same genealogy from Catell to Eliseg, with Vortigern (spelled Gwrtheyrn) as a founder figure, is also found in Jesus College manuscript 20 (see below), but the Jesus College manuscript does not mention Britu. Concenn, Pascent and Maun feature in the Harleian genealogy (see below), there traced back to a founder called Catel Dunlurc (presumably the Catel Drunluc of Historia Brittonum), but there is no mention in the Harleian genealogy of Vortigern or Britu.
Whether St Germanus blessed two dynastic founders, one called Britu commemorated on the pillar and one called Catell mentioned in Historia Brittonum, or a single person bore both names, or one or other source is mistaken, is open to interpretation. Given that Historia Brittonum has a great deal to say about Vortigern, it seems to me likely that it would have mentioned a connection between Catell and Vortigern if such a tradition was widely accepted, so on the whole I think it more likely that two individuals, and by extension perhaps two (or more) interlinked dynasties, are concerned. But this is a matter for interpretation; arguing from absence of evidence should always be approached with caution (!). The location of the pillar is consistent with the medieval territory of Powys.
613 The battle of Caer Legion [Chester]. And there died Selyf son of Cynan.
--Annales Cambriae, available online
Selyf map Cynan can be identified in the genealogies of the kings of Powys (see below). Selyf also appears in the Welsh Triads as a great military leader:
Three Battle-Leaders of the Island of Britain:
Selyf son of Cynan Garrwyn, and Urien son of Cynfarch, and Afaon son of Taliesin. This is why they were called battle-leaders: because they avenged their wrongs from their graves. [?]
--Red Book of Hergest Triads, available online
Since Selyf of Powys was killed fighting at Chester in the seventh century, this may indicate that the territory of seventh-century Powys included Chester. It doesn't guarantee it, as battles were sometimes fought well outside the core territories of the antagonists. For example, according to Bede the Battle of the Idle was fought in Mercian territory between Aethelferth of Bernicia/Northumbria and Raedwald of East Anglia in 616 (Bede, Ecclesiastical History Book II Ch 12). However, presumably Selyf had a reason to be fighting a battle at Chester, and this may have been a territorial interest.
[S]elim map Cínan map Brocmayl map Cincen map Maucanu map Pascent map Cattegirn map Catel dunlurc.
--Harleian Genealogy, available online
Rodri ma6r mab nest merch Cadell Pywys brenhin Pywys.
Cadell M Brochuael M Elisse M Coleda6c M Beli M Seliph M Kynan garwin M Brochuael yscithra6c M manogan M Pascen M Cadell deyrlloch M Cadern M G6rtheyrn g6rtheu
--Jesus College manuscript 20, available online
Selyf map Cynan is recognisable, despite the variant spellings, as Selim map Cinan at the beginning of the Harleian entry, and Seliph M Kynan in the middle of the Jesus College manuscript entry.
Gerald of Wales (Giraldus Cambrensis) was a distinguished Norman-Welsh clergyman who wrote a Description of Wales in the 1190s. He clearly states that Shropshire had previously been part of the kingdom of Powys:
For the country now called Shropshire formerly belonged to Powys, and the place where the castle of Shrewsbury stands bore the name of Pengwern, or the head of the Alder Grove.
--Gerald of Wales, Description of Wales (full text translation at Project Gutenberg)
Pengwern features in the poem Canu Heledd as the court of a leader called Cynddylan. References elsewhere in the poem place Cynddylan in the seventh century and link him to other places in what is now Shropshire (see article on Cynddylan), which is all consistent with Gerald's account. However, Gerald's account was written down a good five centuries after the events of the seventh century, which gives ample time for traditions and locations to become confused, so should be interpreted with caution.
The fourteenth-century Life of St Beuno says of Beuno's father:
There was once a man of lineage in Powys in the place that is called Banhenic, near to the river which was known then as Sabrina and now as Hafren.
--Life of St Beuno, extracts available on Google Books
Later on in the Life, St Beuno is granted land by King Cynan son of Brochwel (who appears in the Harleian genealogies as the father of Selyf ap Cynan, see above), and rebukes the sons of Selyf, prophesying that they and their kingdom will be destroyed.
Sabrina is the Latin name of the River Severn, and Hafren is its modern Welsh name.
Accepting that a fourteenth-century source should be interpreted with caution with regard to events in the seventh century, this suggests that St Beuno was an approximate contemporary of Selyf ap Cynan, and that at that period Powys extended to somewhere on the banks of the Severn. If Banhenic has ever been identified, I don't know of it.
The Severn is a very long river, rising in Mid-Wales on the slopes of Plynlimon, and flowing roughly west through the hills of Powys to Welshpool and then out into the Shropshire Plain, where it describes a leisurely arc round modern Shrewsbury and Wroxeter and then starts flowing south on its way to the Bristol Channel (Severn Sea). In the upper part of its course (roughly, upstream of Welshpool), the Severn flows through the territory of medieval Powys. St Beuno's childhood home may therefore not extend the boundaries of early medieval Powys beyond its medieval counterpart, or it may indicate that early medieval Powys included some of the middle Severn on the Shropshire Plain, as stated by Gerald of Wales.
Ptolemy's second-century geography lists a tribe in west-central Britain called the Cornovii. Their territory included Viroconium (modern Wroxeter), and the fort of Deva Victrix (modern Chester):
From these toward the east are the Cornavi, among whom are the towns:
Deva, Legio XX Victrix
-- Ptolemy's Geography Book 2, available online
If one speculates that the death of King Selyf of Powys at the Battle of Chester indicates that the territory of seventh-century Powys included Chester (see above), and if Gerald of Wales is correct that seventh-century Powys included Shropshire, then this would be consistent with the early medieval kingdom of Powys covering some or all of the lowland territory of the Cornovii as well as the uplands of medieval Powys.
One of the poems attributed to Llywarch Hen in the Red Book of Hergest calls Powys "the paradise of Wales", a name that has, not surprisingly, been adopted as the motto of the modern county (which does not, by the way, follow the boundaries of its medieval counterpart).
Of Powys, the paradise of the Cymry.
--Llywarch Hen, Red Book of Hergest, available online
This is consistent with a territory that included fertile lowland country as well as uplands, although it may reflect polite poetic convention. It's fair to say that describing your patron's country as "paradise" might be a safer bet for a repeat commission than calling it "barren moorland" or even "wild and beautiful uplands", regardless of topographical accuracy.
The place name Powys, which is from the Latin "pagenses" meaning something like "country dwellers", might be considered as evidence against the notion of including the Cornovii and their two towns in the kingdom's territory. It would seem to be more consistent with the rural uplands of the medieval territory of Powys. However, it may be that Powys had multiple rulers (see article on Cynddylan) and that the towns were to some extent self-governing for a while (possibly under the control of urban bishops, see article on "A Bishop of Chester?"), leaving the rural areas of the Cornovii territory to be governed by the rulers of early medieval Powys. In this scenario, the place name could be interpreted as indicating that the towns were treated as separate entities, at least when the kingdom acquired its name.
I think it's a reasonable conclusion that early medieval Powys included roughly the territory of its medieval counterpart in what is now east-central Wales. Historia Brittonum's story of Benlli, the location of the Pillar of Eliseg, and the birthplace of St Beuno according to the medieval Life, are all consistent with this.
Early medieval Powys may also have extended into the adjacent lowlands of Shropshire if Gerald of Wales is correct, if St Beuno's birthplace was on the middle Severn, and if the territories associated with Cynddylan in his praise-poetry were part of the kingdom of Powys. If Chester was in King Selyf's territory, the kingdom may also have included Cheshire in his time.
Powys was evidently a powerful and aggressive kingdom, at least at times. In the poetry attributed to Talisein, Cynan Garwyn (the king who preceded Selyf) is credited with having fought battles in Mona (modern Anglesey), on the River Wye (Gwent, south-east Wales), and "on the hill of Dyved", which could be the territory of Dyfed around what is now St David's in south-west Wales. A king who could fight battles across the length and breadth of what is now Wales, even if they were only raids, presumably controlled considerable resources. This would be consistent with early medieval Powys having controlled the lowlands of Shropshire and/or Cheshire as well as the uplands of its medieval counterpart.
It is worth noting that Gerald of Wales does not say that Powys once included Chester. Caveats about the lateness of the source accepted, this may be an indication that the territory of the Cornovii was at some point divided into two (or more) distinct regions that went politically separate ways.
Trying to define a geographic and political entity that can be labelled 'early medieval Powys' is probably to some extent chasing a chimera. The princes of medieval Wales were forever in territorial dispute with each other, each lord trying to extend his power over his neighbours by military force and/or marriage alliance. There's no reason to imagine that early medieval kingdoms were any more pacific or any less dynamic. It seems likely that the boundaries of early medieval Powys would have fluctuated over time, depending on the relative military and/or political strength of the relevant rulers. The inscription on the Pillar of Eliseg is consistent with this, referring to two kings who had (re)conquered territory that they claimed to have previously been part of their kingdom.
In which case, the lowlands of Cheshire and/or Shropshire and the towns of Wroxeter and/or Chester might have been at some times part of Powys and at other times independent entities or part of other kingdoms, and may have changed hands more than once. Whether such regions were regarded as independent entities that co-operated from time to time (voluntarily or by force) in some sort of confederation called Powys, or as parts of a unified kingdom called Powys that were separated off from time to time (voluntarily or by force), may be a distinction without a practical difference.
For what it's worth, I would identify at least three distinct regions: the upland territory that became medieval Powys; lowland Shropshire; lowland Cheshire. The towns of Wroxeter and Chester may have been independent, or may have been part of the relevant lowland regions. Various combinations of these regions, at various times, under various dynasties, may have been called the kingdom of Powys.
Annales Cambriae, available online
Bede, Ecclesiastical history of the English people. Translated by Leo Sherley-Price. Penguin Classics, 1968, ISBN 0-14-044565-X.
Gerald of Wales, Description of Wales (full text translation at Project Gutenberg)
Harleian Genealogy, available online
Historia Brittonum, available online
Jesus College manuscript 20, available online
Life of St Beuno, extracts available on Google Books
Llywarch Hen, Red Book of Hergest, available online
Ptolemy's Geography Book 2, available online
Red Book of Hergest Triads, available online
Foel Fenlli hill fort You can zoom in and out to place the location in context.
Welshpool Zoom in and out to trace the course of the River Severn
Map showing the county boundaries before the assorted local government reorganisations since the 1960s. Cheshire and Shropshire are numbers 14 and 15. The old county boundaries give a better idea of the approximate location of the Cornovii territories; the modern administrative structure separates out some urban areas as enclaves and can be confusing.