Arthur, King or Warlord
We usually think of King Arthur as a majestic character, who was surrounded by his faithful knights, preferably in shining armour. They would unite around a round table in the great hall of a fortress which we call Camelot, before leaving for some expedition which would take them to the corners of the Isles of Britain.
Well, most of the adventures of Arthur and the Knights of the Round Table were written in the 12th and 13th centuries by authors who used their own world as a model for the times of Arthur. However, this is - of course- complete nonsense, since Arthur lived around 500CE when present Great Britain still was known as the Isle of Britain (or: Isle of Mighty), at the end of the Roman Empire and the beginning of the Merovingian period. The time interval is seven centuries.
During the last decades the occupation of Britain by the Romans, the Saxons had their try - they started attacking the Armorican coasts. To ensure the defense of the coastline, the Romans called upon the Breton islanders. From the 3rd century, many of them came to settle in the north of the Armorican peninsula. This was the beginning of the Breton emigration, and it had the benediction of the imperial authorities. In addition to that, in 410, the emperor Honorius, realising that the legions were not sufficient enough in number on the Island of Britain, called them back onto the continent, confiding the entire defense of the Island to the Britons, as citizens of the Roman Empire. This edit of Honorius explains the events in the middle of the 5th century perfectly, when the Briton king Vortigern (also known as Gwrteyrn), probably a usurper, called upon the Saxons, as well as the Jutes and the Angles who were allies and made the most of the situation in 446CE. They were well paid and occupied numerous regions of the Island.
It was at this time that the Arthurian period began.
Arthur according to Nennius