The Sword and the Circle — Rosemary Sutcliff

His kingdom was magical, his knights were loyal, and his life was filled with adventure....

young Arthur Pendragon became High King of England the instant he pulled the mysterious sword from the stone. He unlocked the magic within the sword Excalibur, and won the heart of the Lady Guenever. At his side through quests and adventures were the Knights of the Round Table -- among them Gawain, who faced certain death at the hands of the Green Knight; Percival, who learned that it took more than victory on horseback to win a place at the Round Table; and Lancelot, who daily felt a passion he was forced to hide. Arid over them all ruled Arthur, true King... .