Many people assume that a fictional work is done without research. I read more than 3 dozen books about King Arthur and general Celtic myth for my books Lancelot, Arthur Rex Eternus, The Quest of Arthur, King of Ages, and with a focus on non-Arthur Celt myth and legend, Mythic Memories, Sacred Ground, and Visitations into Sidhe and Tir na nOg. It is the fact that the more true the setting you create feels, (verisimilitude) the more depth the characters you create or use will become.
― Howard Pyle, The Story of King Arthur and His Knights
To that extent, my studies focused mostly upon the history that is known, the history that was speculative, and the historical studies that regard the era. Roman Britain is an area of writing that fascinates me, it moves me, from both sides of the conflict. The fact that Arthurian legends place a real Arthur, a war general, shortly after Roman withdrawal from Britain suggests that the real life Arthur had been a Britain officer in a Roman Legion. Perhaps he had risen as a result of being left behind as a leader to be certain of his loyalty to Rome, but it is more likely that he'd been trained and fought at the side of the Romans.
“Yet some men say in many parts of England that King Arthur is not dead, but had by the will of our Lord Jesu into another place; and men say that he shall come again, and he shall win the holy cross.” Thomas Malory, Le Morte d'Arthur
Arthurian legend has roots in Britain, as it was a story of pride, tragedy and romance. A piece of evidence towards the legend having roots in reality, Glastonbury Tor is where Arthur and his queen's bodies were said to be unearthed. When the legend says he died in Avalon, an island of apple trees and beauty, surrounded by mist. Glastonbury Tor is a great hill, which is circled on either side by rushing rivers. In the morning dew, mist, Glastonbury looks very much like an island, surrounded by mists.
“Alas that he did not ask the question then! I still sorrow for him on that account. For when the sword was put into his hand, it was a sign to him that he should ask. And I pity too his sweet host whom God's displeasure does not spare and who could have been freed from it by a question.”
Wolfram von Eschenbach, Parzival
"It's obvious that it's after dinner," says sir Kay unable to hold his tongue. "There are more words in a potful of wine than in a barrel of beer". Chrétien de Troyes