Once the Anglo Saxon Germanic tribes had established control over what is now England, the Brythonic Celts were confined to the Western areas of Wales, Cornwall and Northern Britain.
In Wales, this was a period when local chieftains ruled, squabbled and sometime grew in power. The Welsh tradition of dividing a father’s lands evenly between his sons often resulted in sibling rivalry and a grasp for power.
This was also the start of a series of Viking raids, where they plundered many coastal monastic sites.
What is now Treoes lay in the small Celtic kingdom of Cernyw, a western chunk of the former Silures territory
In around 420 AD Cernyw was subjected to a series of fierce raids along its coastline. Irish raiders sailed up the Severn and seized a large amount of booty in the form of corn and cattle; they also took children and women as slaves. There are legends that they kidnapped the young St Patrick from the College at Llantwit Major.
In 437 AD Cernyw and the adjoining territory of Ewyas were combined by Owain Finddu (Owain Black Lips in Welsh), who was possibly the son of the most powerful Romans in Britain, Magnus Maximus. (Magsen Wledig in Welsh).
In 470 AD Glwys came to power and Cernyw was renamed Glywyssing in his honour. For the next 100 years Glwysiog was ruled as three territories with an overlord controlling the entire territory. These comprised of:
- Gwynllg which formed the far eastern part of Glywyssing, divided from Gwent by the River Usk, with a capital at Allt Wynllyw on Stow Hill (in Newport)
- Penychen divided from Gwynllg by the River Elerch, otherwise known as the Greater Rumney, which was ruled from Nant Pawl.
- Gorfynedd the westernmost section, which included what is now Glamorgan and the Gower Peninsula and which was ruled from Llaniltud Fawr (Llantwit Major).
In 580 AD the King of nearby Gwent, Meurig, gained control of Glywyssing through marriage and unified the two Kingdoms until 745 AD.
In 735 Ithel ap Morgan became ruler of Gwent, Glywyssing and Ergyng and therefore King of all of South-East Wales. Around this time Gwent extended east of the River Wye into what is now the Forest of Dean.
Around 745 Ithel divided the joint kingdom between sons, with Brochwal ap Ithel ruling Gwent and Rhys ap Ithel ruling in Glywyssing. Ithel made sure that he was recognised as their overlord.
The Kingdom remained relatively stable throughout the remainder of the eighth and into the ninth century.
In 942 AD Morgan Hen Fawr (Morgan the Old), became king of Glywyssing and Gwent under the new name of Morgannwg (modern Glamorgan).
At this time the Saxons in England were gaining in power and Morgan was subjected to the over lordship of Athelstan, who was based in Hereford.
The Kingdom once more broke up after the death of Morgan in 972 AD, but a new force was about to the exerted on the area.
In 1055 AD Gruffudd ap Llywelyn conquered all of what is now Wales.
He was the only King to control all of the country – from Anglesey to Glamorgan.
This was therefore a period of great turbulence, with territories changing hands often. For the most part. the Welsh Kings had kept the Saxons at bay, remaining largely independent until 1066 AD, when everything changed for the Anglo Saxon, and later for the Welsh as well.
In 1066 AD the Saxon King Harold Godwinson was defeated by William Duke of Normandy. The Normans rapidly established control over England, becoming the aristocratic rulers of the Anglo- Saxons.
Wales remained independent, but William had rewarded his most loyal general with large territories along the border between England and Wales. These were know as the Welsh Marches and the nobles had the authority to keep their own armies – with the primary focus of ensuring the Welsh were not posing a threat.
There was however a quiet migration to the Vale of Glamorgan of people of Irish, Norse and Anglo-Saxon descent from places such as Somerset. The Vale thus became an area of mixed population, with some unsympathetic to the cause of Welsh Independence who were happy to acquiesce to Norman rule when it came.