The Written Record
Most historians consider Geoffrey of Monmouth's History of the Kings of Britain to be the starting point of the modern Arthurian Legend. It was Geoffrey's History that was the first to spread tales of Arthur and his knights across Europe, and it was also his History that was the first to present Arthur as the king of a great empire, the pinnacle of civilization. As such, it makes sense to start there when looking for clues about an historical Arthur.
The problem, of course, is that Geoffrey distorted much in order to piece together his narrative, and he cannot be considered reliable by any means. Still, it is clear that much of his work is, at least in part, based on older, Celtic and Welsh folklore, or in some instances, genuine history. An example is the king Constantine, whose son was a monk named Constans. This was the Briton crowned emperor who, with his son, the monk, took the Roman troops out of Britain, and marched on Spain. This figure did exist, although in Geoffrey's work, he became the grandfather of King Arthur. Another, more notable character is a chieftain named Vortigern, whom we have already seen.
What, then, do the early records say of Arthur? Hardly anything, and that is the problem. If Arthur had been a real king, especially one remembered in legend for so long, then we would expect to find countless records of him, and there are hardly any. Most of the ancient texts that do mention him more closely resemble fairy tales than history. Some historians take this to mean he never really existed, and that his legend is just a myth. But others argue that this only means his legend became inflated very quickly, with still others arguing that he is mentioned in the records; just as a different person who came, through some means or another, to be called Arthur later on down the line.
One early source which mentions Arthur by name is the tenth–century document the Annales Cambriae ("Annals of Wales.") This is a chronicle of obscure Welsh tales, but Arthur is mentioned in it twice. In the year 516, the Cambriae records:
"The Battle of Badon, in which Arthur carried the Cross of our Lord Jesus Christ for three days and three nights on his shoulders and the Britons were the victors."
Although this tale is clearly unbelievable, most historians believe the Battle of Badon really did take place, and other sources associate it with Arthur as well. Twenty–one years later, the Cambriae records:
"The battle of Camlann, in which Arthur and Medraut fell: and there was plague in Britain and Ireland."
It is interesting to note that all the characters in the Cambriae except for Arthur, Medraut, and Merlin, are real people who are known to have lived. Some historians have argued that this proves Arthur and Merlin were real. However, this argument is no longer widely accepted, because early legends of Arthur were already flourishing when the Cambriae was written, as shown by the reference to Jesus Christ's cross. Thus, the author could easily have believed these characters were real people, and added them to the chronicle.
Most of the other tales to mention Arthur from this time are fantastical. One example is the story Culhwch and Olwen, believed to be the oldest Arthurian romance, with some scholars putting it even before Geoffrey of Monmouth's History. Culhwch and Olwen is a tale about how a man named Culhwch enlisted Arthur's help in performing a series of quests to win the hand of his love, Olwen. This tale is much more fantastical than later Arthurian romances, with characters possessing superhuman powers, fighting giants, and so on.
Another text, The Book of Taliesin, attributed to a sixth–century poet, but available to us only in a fourteenth–century manuscript, contains an interesting story about Arthur traveling to the land of Annwn to seek out a magical sword and cauldron (believed by some to be the precursor to the Holy Gail). Indeed, many ancient Welsh poems and myths depict Arthur as being much more of a supernatural being, with one legend portraying him as a lord of the Underworld. It is for this reason that many historians once believed Arthur was merely the personification of an ancient Celtic god. However, this theory is no longer widely accepted because it would be highly unusual for a Celtic god to be given a Roman name, or to become as widespread as Arthur's legend became.
The Life of Saint Cardoc, written about 1130, portrays Arthur in a negative light, and tells a story about how he contested the saint's right to give seven years of shelter to a man who had killed three of his soldiers. After a dispute, he is granted a herd of cattle as compensation, but the herd magically turns into fern as soon as he gets it. Geoffrey Ashe has identified two other monastic texts which portray Arthur in a negative light, and notes that one of them refers to him as a tyrant – that is, a despot who rules without authority. Ashe has speculated that this may indicate the historical Arthur was a local despot who rose to power, but had no legitimate claim to it. Ashe also suggests this may indicate he repossessed Church property in order to pay for his campaign. Ashe points to another period in history where something like this did happen. In 732, Charles Martel uplifted property from the Church in order to fight off invading Arab soldiers. Even though he effectively saved his Christian city from invasion, he is remembered negatively in monastic writings.