Vortigern is traditionally the fifth-century king who invited the Anglo-Saxons over to the British Isles and in the process initiated their conquest of England. However, it’s a faulty tradition.
That emerges in a study of the sources he appears in. A common myth is that Vortigern is first mentioned in Gildas’ De Excidio Britanniae. He does not. Gildas’ information becomes shaky in the middle of the fifth century, before which a “superbus tyrannus” is mentioned in conjunction with the invitation to Anglo-Saxon mercenaries. Coincidentally, the title means great king. Vortigern, and the Welsh equivalent Gwrtheyrn, also translates as great king.
Vortigern first appears with Bede some three hundred years after his supposed life. Here we are given an exact reiteration of what is found in Gildas. Which means only that Bede assumed that Gildas meant Vortigern when he wrote superbus tyrannus.
The next source that names him is Historia Brittonum, a book written in Gwynedd. Those copied directly from the original manuscript do say Vortigern invited the Anglo-Saxons Hengest and Horsa, a la Gildas. However, they also credit him with founding the Powys dynasty. Powys, coincidentally, was a close ally to Gwynedd at the time of the book’s creation.
This book is where all the truly nasty accusations – his poor judgment with Hengest, his foolish dowry of Kent, his inability to control the Anglo-Saxons or even his own people, or his sexual relationship with his daughter. But the original history was written in roughly 829, and all the versions where this new information is given are based on a tenth century version. This updated Historia Brittonum was written in Dyfed. In the tenth century, Dyfed was attempting to unite all of the British kingdoms. It could not rewrite history regarding Gwynedd as Dyfed’s dynasty was closely related to the Gwynedd family. However, Dyfed could attack Powys. By adding so much negative press to his story, it did just that.
Incidentally, The Anglo-Saxon Chronicle also mentions Vortigern. The initial note is taken directly from Gildas, or Bede. After that, there are several battles taken from Historia Brittonum.
In sum, Gildas made up history during the mid-fifth century and before because he did not have any. But he did not mention Gwrtheyrn. All historical sources that followed were based on an assumption that Gildas had meant Vortigern. As they were clearly wrong, Vortigern’s place in the historical record is uncertain.
The Welsh geneologies, once resolved of inconsistencies by Dr. Molly Miller, give a clear chronology for the infamous Powysian king; he lived in the middle of the sixth century. As a man living in the sixth century and not the fifth he could not have taken part in the legend of Hengest and Horsa. And, as all the most vicious stories about Vortigern were written by Dyfed during its dynasty’s attempts to usurp control of Powys, the claims of Vortigern’s incompetence, stupidity, and incestuous relationship cannot be accepted without discussion.