It very roughly covered the northern two-thirds of the modern county of Powys and part of today's English West Midlands (see map).

[4] Throughout the Early Middle Ages, Powys was ruled by the Gwertherion dynasty, a family claiming descent jointly from the marriage of Vortigern and Princess Sevira, the daughter of Magnus Maximus.

[5][6][7] Archaeological evidence has shown that, unusually for the post-Roman period, Viroconium Cornoviorum survived as an urban centre well into the 6th century and thus could have been the Powys capital.

At the commencement of the battle, Bede tells us that the pagan Æthelfrith slaughtered 1,200 monks from the important monastery of Bangor-on-Dee in Maelor because, he said, "they fight against us, because they oppose us by their prayers".

According to the probably ninth-century cycle of englyn-poems Canu Heledd, the region around Pengwern was sacked soon after, its royal family slaughtered and most of its lands were annexed by Mercia, some by Powys.

However, this account is generally now thought to represent ninth-century imaginings of what must have been going on in the seventh, inspired by Powys's political situation in the ninth century.

This endeavour may have been with Elisedd's own agreement, however, for this boundary, extending north from the Severn Valley to the Dee estuary, gave Oswestry (Welsh: Croesoswallt) to Powys.

Davies wrote of Cyril Fox's study of Offa's Dyke, "In the planning of it, there was a degree of consultation with the kings of Powys and Gwent.

On the Long Mountain near Trelystan, the dyke veers to the east, leaving the fertile slopes in the hands of the Welsh; near Rhiwabon, it was designed to ensure that Cadell ap Brochwel retained possession of the Fortress of Penygadden."

Merfyn inherited Powys, whilst his brothers, Anarawd ap Rhodri and Cadell, established the Aberffraw dynasty in Gwynedd and the line of Dinefwr respectively.

In 942 Hywel Dda of Deheubarth (Rhodri's grandson through his second son, Cadell) seized Gwynedd on the death of his cousin, Idwal Foel.

Hwyel's works would lead posterity to name him the good (Welsh: Hywel Dda), and his reign is recognised as an unusually peaceful one.

Llywelyn's son Gruffydd would unite all Wales under his own kingship, displacing his cousins in Deheubarth, even expanding into England and affecting politics there.

It is through Princess Anghared (as daughter of Maredudd ab Owain of Deheubarth and Powys), her second husband was Cynfyn ap Gwerstan, that the Mathrafal dynasty was founded.

Roger Montgomery rose in revolt against King William II of England, and his son Robert Belleme had his lands confiscated in 1102.

Through the twelfth and thirteenth centuries the House of Mathrafal struggled to retain its lands in Powys against Norman Marcher lords and a resurgent Gwynedd.

By this time, Gruffydd's son, Owain, had chosen to anglicise his name to Owen de la Pole (taking the surname from the capital of Powys Wenwynwyn – Pool).

However, when the child's body was discovered in the River Dee four years later and presumed murdered, Mortimer was allowed to take the lands – the cantref of Swydd y Waun.

The Barony survived until the rebellion (in nominal support of King Richard II's heir) of Owain Glyndŵr, the great-grandson (or great-great-grandson) of Gruffudd Fychan.

This made him a vassal of Edward I, enabling him to rely on English support to keep him in power, while otherwise remaining completely independent (like other Marcher Lords).

The name Powys for this area disappeared (at the latest) with the introduction of the Laws in Wales Acts 1535–1542 when its marcher lordships were incorporated into counties.

However, Brecknockshire had not traditionally been within the bounds of the old kingdom, Radnorshire had not been part of it since the mid-10th century (if it ever had before, rather than just held by family members), and most of what had once been Powys Fadog was placed in the new county of Clwyd.