"The Skystone" by Jack Whyte. This book is the first in a series about King Arthur. The twist is that King Arthur is not a main character until much later in the series. It is the story of his great-grandfathers, grandfathers, and father and how they built "Camulod" (Camelot). It also gives realistic explanations to the "magic" from this story. For example, it will explain who the Lady of the Lake is and why Excalibur is so special. The author also pays close attention to writing historically correct details. Even though it is Historical Fiction, it will give you a very plausible explanation about King Arthur and how he may have lived.