The era now thought of as the Early Middle Ages began when Roman Emperor Honorius withdrew Roman troops from Britannia in 409CE. He told the British city-regions (civitates) to take care of their own defences.
So the Roman governance structure of five Provinces and 28 civilian city-regions remained in place, but with freedom from Rome.
BATTLE OF WALLOP
The first recorded conflict arising from this was the Battle of Guoloph, mentioned in the Historia Brittonum. The opposing generals in this battle were Vortigern and Emrys Wledig (whose name when Latinised becomes Ambrosius). http://earlybritishkingdoms.com/archaeology/wallop.htm outlines a good case for reckoning that
(a) the battle was fought at Chattis Hill, which is on the borders of Nether Wallop and Broughton;
(b) Emrys commanded and had refortified the nearby Danebury hillfort (in the Parish of Nether Wallop) as a caer (hillfort/royal residence); and
(c) the battle was fought in 437CE.
VORTIGERN AND EMRYS
Vortigern apparently won this battle, but Emrys cannot have been decisively walloped, for the Hisotria records that Vortigern remained afraid of Emrys afterwards.
It is pertinent that this location was close to the Roman Provincial border between Britannia Prima and Maxima Caesariensis. Prima comprised Wales, Cheshire, most of the West Midlands, and the Westcountry including the Cirencester city-region; Maxima was the south-east of the island including the Silchester and Winchester city-regions covering Hampshire and Berkshire.
Vortigern is known to have fought battles in Kent and other parts of Maxima to try to drive off Saxon raiders. (I use the word ‘Saxon’ the way the Britons did, to refer to any and all the Germanic tribes that disturbed Britain.) Emrys Wledig is associated in legend with Eryri (Snowdon) and with Brycheiniog (now SW Powys). So it is quite possible that Vortigern was de-facto ruler (Governor) of Maxima and Emrys was similarly de-facto ruler of Britannia Prima…. both before and after the battle. Both men’s titles imply some such large area of power: Vortigern means “High King”; wledig means “great ruler”.
Vortigern may have presented himself as ruler of all Britain, but where is the evidence for his having any power or influence outside the south-east? The Roman Province of Flavia Caesariensis comprised the four city-regions centred at Brough-on-Humber, Leicester, Lincoln, and Buxton. The two east-coast city-regions, those centred on Lincoln and Brough, seem to have passed peacefully into Saxon control soon after the departure of Honorius’s legions – their territories becoming, respectively, the kingdoms of Lindsey and Deira. Archaeology at Hessle in the East Riding shows that there was no disruption of land usage in the 5th century, in contrast to the Vikings’ impact in the 9th. The dating of the Saxon building of a village at West Stow to c420CE (see https://www.weststow.org/Anglo-Saxon-Village) points to a similarly peaceful transition to Saxon rule in East Anglia.
By contrast, the Britons retained control of all the city-regions of the Province of Britannia Secunda (the North, from the Mersey and South Yorkshire to Hadrian’s Wall), and in the Province of Valentia (everywhere between Hadrian’s Wall and the Antonine Wall), until at least the 570s – and with no sign in those regions of Vortigern.
Gildas, in his book written in the sixth century, highlights and criticises Vortigern’s invitation to Saxons led by Hengist to help him fight against Irish and Pictish raiders after 446CE. This was retrospectively interpreted as the start of a slippery slope to the Saxon control of about a dozen city-regions around the coast from East Yorkshire to Hampshire that was his sixth-century reality. Easy to be wise after the event!
ANNALES CAMBRIAE
One version of the Annales Cambriae (British annals) records that decision of 446. The version historians see as earlier and more reliable (the Harleian “A” manuscript) does not, but I suspect only becasue the line for Year 1 of its annals is missing. Year 1 is undoubtedly in the 440s and the fateful invitation to Hengist is the most obvious event in that decade to have started the Annals with. The fifth century and early sixth century entries fit best to the assumption that they translate into AD dates on the basis that Year 1 of the Annals in that era was 446CE.
I have shown as best I can in a previous post here how I figure that Glastonbury Abbey was founded in the 440s and that St. Patrick returned from Ireland in c445 to be its first Abbot. This accounts for the absence from the Annals of Germanus’s visit to Britain as both a general and a bishop propagating the form of Christianity the Pope favoured.
I also, more speculatively, reckon that the early entries in the Annals – those wholly in Latin, as distinct from the Cambrian-Latin hybrids of many entries from 538CE (the Battle of Camlann) onwards – were sourced from records kept at that abbey – quite possibly indeed, as suggested half a century ago (I think by Alcott), in the margins of tables used for calculating the date of Easter.
CADOR
At least five hillforts in the Westcountry are called Cadbury: three in Somerset, one in east Bristol, and one in mid Devon. Presumably named after a fifth century warrior named Cador or Cado. Caradoc of Llancarfan names a Cado as a king reigning later in the century as an old man when Carantoc became a Christian leader in his kingdom. His caer (hillfort, royal residence) at the time was Dundry, in Somerset on the southern edge of Bristol. It is rational to suppose that he could have been reigning for three or four decades before that, which takes us back to the 440s or even the 430s. I have indicated in another post here that I interpret Cador to have been a very effective defensive strategist, keeping the city-region of Lindinis (Somerset and surrounds) free from Irish raiders and pirates – a goal calamitously not met by whoever was in charge at Ilchester in c398.
Caradoc wrote that when Carantoc visited Dundry, Cador was the honoured Governor of Lindinis (to call him a king would be an anchronism), but Arthur was in the meeting with him as a youth, apparently as Cador’s heir-apparent. So Cador is, for Lindinis, the bridge between governance under Rome and under King Arthur.
AMBROSIUS and ARTHUR
A general whose name in Latin was Ambrosius Aurelianus came to power in the late fifth century; most likely in 479. He was presumably a son, grandson, or other close relative, of Emrys Wledig. Like the first Emrys, his base was western Britannia – the Roman Province of Britannia Prima.
The next decade was the period when, Gildas tells us, there was war between Britons and Saxon raiders and each side won some of the battles.
In 490 the Britons won the decisive battle “on the Badonic hill”. It was followed by half a century of peace between the (nominally still Roman) Britons and the barbarian Saxons. Badonic means in the special-status civitas of Bath and its immediate surrounds. Arthur is credited with achieving that victory, both by British (and Breton) poets and minstrels in the following centuries and by the early-12th-century neutral (being neither Briton nor Saxon, but Norman) history writer William of Malmesbury. William says that Ambrosius was the leader of the Britons at that time but Arthur won this battle victory.