517-49 - King Maelgwn flourishes in Gwynedd. Invades Dyfed and generally tries to assert himself as a High-King in Britain.

519 - The Kingdom of the Wessex is founded with Cerdic, a leader probably of mixed Saxo-Celtic birth.

c.520 - Death of King Aergol Lawhir of Dyfed. He is succeeded by his son, Gwerthefyr the Protector. Death of King Lleinog of Elmet. He is succeeded by his son, Gwallog Marchauc Trin. Possible daeth of King Cunbelin, perhaps of the Peak District. His kingdom may have been seized by his brother, Pabo. This would explain why Cunbelin's son, Cynwyd, and his descendants settled further south, as Cynwyd and his followers, the Cynwydion, would have been obliged to seek lands elsewhere. Death of King Riwal Mawr Marchou of Domnonée. King Teudric returns to Cornouaille and defeats and kills King Macliau and his eldest son, Jacob in battle. Macliau's son, Waroc is allowed to remain as King of Broërec. St. Dyfrig establishes a bishopric in Gwent & Ergyng.

521 - St. Samson is consecrated a bishop by St. Dyfrig, Bishop of Gwent & Ergyng.

c.522 - King Teudric of Cornouaille dies and is succeeded by his brother, Meliau.

c.523 - Death of King Gwynllyw of Gwynllwg. Gwnllywg and Penychen are united under his son, St. Cadog.

c.525 - King Pabo Post Prydain of Craven in the Pennines abdicates his throne in order to retire to a hermitage on Ynys Mon (Anglesey). He divides his kingdom between his two sons: Dunaut Fwr and Sawyl Benuchel. The former founds Dunoting in the North while the latter holds the Peak District in the South. St. Samson founds the Monastery of Dol and becomes its first Abbot. Prince Rivod of Cornouialle murders his brother, King Meliau, and usurps the Throne.

c.528 - King & Saint Cadog of Gwnllywg & Penychen abdicates in favour of King Meurig of Gwent, who is joined in marriage to Cadog's aunt. Banishment of Princess Teniu of Gododdin. Birth of her son, St. Kentigern.

530 - Saint Pabo Post Prydain, former King of the Pennines dies at Llanbabo. The British of the Isle of Wight are defeated by King Cerdic of Wessex at the Battle of Carisbrooke.

c.530 - St. Ninian founds the cathedral at Whithorn. He is opposed by King Tutgual Tutclyd of Strathclyde.

c.535 - Kings Sawyl Benuchel of the Southern Pennines is expelled from his kingdom (enemy uncertain) and flees to Powys. The Anglians of Mercia probably move into the area. Death of King Cynfarch Oer of North Rheged. He is succeeded by his son, Urien Rheged. Death of King Meurig of Glywysing & Gwent. He is succeeded by his son, Erbig. Death of St. Illtud, Abbot of Llanilltud Fawr.

537 - Battle of Camlann (according to the Annales Cambriae which may record the event up to twenty years late), fought between the forces of Arthur and the rebellious Medrod. Death of both. Saint and King Constantine, ruling in Dumnonia, takes on the High-Kingship, probably only nominally.

c.538 - King Cynlas Goch of Rhos abandons his wife in favour of his sister-in-law, a nun who he drags from her convent. Civil War between Cynlas and his cousin, King Maelgwn of Gwynedd. Maelgwn enters a monastery, but soon returns to secular life and murders his nephew in order to marry his widow. Civil War also in Powys due to the tyranny of King Cyngen Glodrydd.

540 - King Jonas of Domnonée is murdered by King Cono-Marc of Kernow (Cornwall) and Poher. Cono-Mark marries Jonas' widow and rules Domnonée.

c.540 - Probable writing of Gildas' 'De Excidio Britanniae'. King Caradog Freichfras of Gwent gives Caerwent to St. Tathyw and moves the royal court to Portskewett. Death of King Cedic of Strathclyde. His kingdom is divided between at least two of his sons: Tutgual Tutclyd retains central Strathclyde, while Senyllt receives the area around Selkirk. Death of King Elidyr Llydanwyn of South Rheged. He is succeeded by his son, Llywarch Hen. Death of King Eliffer Gosgorddfawr of Ebrauc. He is succeeded jointly by his sons. Peredur & Gwrgi.

c. 545 - The Synod of Brefi is held at Llandewi Brefi to condemn the Pelagian heresy. St. Dyfrig, Bishop of Gwent & Ergyng resigns his supposed position as 'Archbishop of Wales' in favour of St. David. David supposedly moves the Archdiocese from Caerleon to Mynyw (St. David's). Death of King Erbig of Glywysing & Gwent. He is succeeded by his son, Erb. Death of King Gwerthefyr of Dyfed. He is succeeded by his son, Cyngar. Death of the wandering King Cynwyd Cynwydion. He is succeeded by his son, Cadrod, who settles their people amongst the Chiltern Hills in a kingdom which becomes named Calchfynedd after them. Prince Judwal of Domnonée flees from his murderous step-father to the court of King Childebert of the Franks.

546 - St. Cadog returns to Brittany.

547 - The King of Bryneich, probably Cuncar, is expelled from his fortress of Bamburgh by King Ida of Bernicia.

c.548 - King Cono-Marc of Kernow (Cornwall), Poher and Domnonée marries Princess Triphine of Broërec.

549 - A 'Yellow' Plague hits the British territories, causing many deaths, including King Maelgwn of Gwynedd. Ireland is also affected. The Saxons in the south and Anglians in the east seem to be unaffected by it.

c.550 - Death of St. Ninian, Bishop of Whithorn. King Senyllt of Galwyddel is expelled from the mainland portion of his kingdom by the forces of King Tutgual Tutclyd of Strathclyde. He flees with his family to Ynys Manaw. In the confusion, Prince Gwenddoleu of Ebrauc seizes the area around Caer-Wenddoleu (Carwinley). A probable land shortage in Strathclyde forces Prince Clydno to invade Gododdin and take control of Din-Eidyn (Edinburgh). The Birth of St. Tremeur. Murder of his mother, Triphine, by his father, King Cono-Marc of Kernow (Cornwall), Poher and Domnonée. Prince Judwal of Domnonée retakes his throne. Cono-Mark flees to Cornwall. The legendary Kingdom of Lyonesse is inundated by the Sea. Prince Teilo of Ceredigion establishes the diocese of Llandeilo Fawr with himself at first bishop. Death of St. Dyfrig, Bishop of Gwent & Ergyng. He is succeded by Bishop Gwrfan.

552 - King Cynric of Wessex lays siege to the British at Old Sarum and put them to flight.

c.553 - St. Kentigern Garthwys founds Glasgow Cathedral, adjoining a Christian cemetery established by St. Ninian at the request of the local monarch, possibly Prince Riderch Hael of Strathclyde.

c.554 - Death of King Tutgual Tutclyd of Strathclyde. The kingdom is probably divided between his sons, Morcant Mwynfawr & Riderch Hael.

555 - St. Cybi Felyn, Abbot of Holyhead, dies at his monastery. Murder of St. Tremeur. Death of his father, King Cono-Marc of Kernow (Cornwall) and Poher.

c.555 - Death of King Erb of Gwent. The kingdom is divided into Gwent and Ergyng. St. Kentigern Garthwys, Bishop of Glasgow, tours his diocese and is opposed by King Morcant Mwynfawr of Lesser Strathclyde.

556 - King Cynric of Wessex lays siege to the British at Barbury Castle and is victorious.

558 - Broërec is attacked by King Childebert of the Franks. King Canao II leads resistance.

c.560 - Prince Elidyr of Strathclyde invades Gwynedd in right of his wife. He tries to expel his brother-in-law, King Rhun Hir of Gwynedd, at the Battle of the Cadnant Brook, but is killed in the process. Due to heightened persecution by King Morcant Mwynfawr of Lesser Strathclyde, St. Kentigern Garthwys flees his Glasgow diocese for the safety of South Wales, before moving northwards to Llanelwy (St. Asaphs).

564 - Death of St. Tugdual, Bishop of Tréguier.

c.564 - St. Cadog settles in Weedon in Calchfynedd and is made Bishop there. St. Samson attends the Council of Paris and witnesses several royal decrees.

c.565 - Death of King Cyngar of Dyfed. He is succeeded by his son, Pedr. King Riderch Hael of Strathclyde mounts an unsuccessful revenge attack on King Rhun Hir of Gwynedd. Rhun marches on Strathclyde and reinforces the armies of his half-brother, Brudei, in Pictland. Death of St. Samson. St. Gildas retuns to Ireland for a while and then retires to Llantokay (Street) in Glastening.

569 - St. David holds the Synod of Victoria to denounce the Pelagian heresy once more.

570 - Death of St. Gildas at Llantokay (Street). He is buried at Glastonbury Abbey.

c.570 - Death of King Gwallauc Marchauc Trin of Elmet. He is succeeded by his son, Ceretic.

c.570-75 - The Northern British Alliance is forged between the kingdoms of North Rheged, Strathclyde, Bryneich and Elmet. They fight the Northumbrians at the Battles of Gwen Ystrad and the Cells of Berwyn

571 - King Cuthwulf of Wessex invades Midland Britain and conquers the British, probably under King Cadrod of Calchfynedd, at the Battle of Bedford.

573 - Kings Peredur and Gwrgi of Ebrauc ally themselves with Kings Dunaut Fwr of the Northern Pennines and Riderch Hael of Strathclyde. They march north to claim the fort at Caer-Laverock from King Gwenddoleu of Caer-Wenddoleu. The latter is killed in the Battle of Arderydd (Arthuret) and his bard, Myrddin, is forced to flee into the Caledonian Forest.

574 - St. Kentigern Garthwys leaves his Northern Welsh diocese of Llanelwy (St. Asaphs) in the hands of St. Asaph and returns to Strathclyde to reclaim the Bishopric of Glasgow.

c.574 - After defeating King Gwenddoleu, the security of Strathclyde is at a low ebb. King Urien of North Rheged takes advantage of the situation and conquers Galwyddel.

575 - Prince Owein of North Rheged kills King Theodoric of Bernicia at the Battle of Leeming Lane.

c.575 - Death of King Erb of Glywysing & Gwent. His kingdom is divided between his sons: Nynnio takes the greater kingdom & Peibio Clafrog receives Ergyng.

577 - Wessex invades the lower Severn Valley. Kings Ffernfael of Caer-Baddan (Bath), Cyndyddan of Caer-Ceri (Cirencester) and Cynfael of Caer-Gloui (Gloucester) are killed at the Battle of Dyrham. Wessex overuns the Cirencester area.

580 - The army of Kings Peredur and Gwrgi of Ebrauc march north to fight the Anglians of Bernicia. Both are killed by King Adda's forces at Caer Greu. The Deirans rise up, under King Aelle, and move on the City of Ebrauc. King Peredur's son is forced to flee the Kingdom. St. Cadog is martyred in Calchfynedd by invading Mercians.

c.580 - Death of Bishop Gwrfan of Gwent & Ergyng. He is succeeded by Bishop Elwstyl.

584 - Death of St. Deiniol Gwyn, Bishop of Bangor Fawr. The British are victorious over King Ceawlin of Wessex at the Battle of Fethanleigh and kill his brother, Cuthwine. Ceawlin ravages the surrounding countryside in revenge.

585 - The Siege of Ynys Metcaut (Lindisfarne). The Northern British Alliance (North Rheged, Strathclyde, Bryneich and Elmet) lays siege to King Hussa of Bernicia and almost exterminates the Northumbrians from Northern Britain. King Urien of North Rheged is assassinated at the behest of his jealous ally King Morcant Bulc of Bryneich. The Northumbrians recover while internal squabbles tear the British Alliance apart.

c.585 - Death of King Pedr of Dyfed. He is succeeded by his son, Arthur.

586 - Death of King Rhun Hir of Gwynedd. Death of King Judwal of Domnonée.

588 - King Edwin of Deira is ousted from his Kingdom by the Bernicians and seeks refuge at the court of King Iago of Gwynedd.

589 - Death of Saint and King Constantine of Dumnonia. Death of St. David, Bishop of Mynyw (St. David's).

c.591 - King Dunaut Fwr of the Northern Pennines mounts an invasion of North Rheged, but is repulsed by its King, Owein, and his brother, Prince Pasgen. Prince Elffin of North Rheged is simultaneously attacked by King Ceretic of Elmet.

c.593 - King Morcant Bulc of Bryneich invades North Rheged and kills King Owein in battle. Prince Pasgen of North Rheged flees to the Gower Peninsula. A greatly diminished North Rheged probably continues under the rule of their brother, Rhun.

595 - The aging King Dunaut Fwr of the Northern Pennines dies fighting off a Bernician invasion. His kingdom is overrun and his family flee to join his grandson in Gwynedd.

c.595 - Death of King Nynnio of Glywysing & Gwent. He is succeeded by his son, Llywarch. Death of St. Teilo, Bishop of Llandeilo Fawr. His successor is unknown. Death of Bishop Elwstyl of Gwent & Ergyng. He is succeeded by Bishop Arwstyl.