Sword at Sunset is a best-selling 1963 novel by Rosemary Sutcliff. One of her few historical novels written specifically for adults, it is her interpretation of the legend of King Arthur.
This is the first novel that Sutcliff wrote using a first-person singular point of view for her story. In an interview with Raymond H. Thompson (in 1986), she explained that she actually spent the eighteen months while writing this story thinking like a man and felt that the story was being fed to her.
Unlike most of the The Eagle of the Ninth series, it does not follow either the inheritor of the dolphin seal ring or the person who will eventually marry said inheritor; although the current inheritor, the son of the protagonist of The Lantern Bearers, is a minor character in the book, the action follows the character of Artos (Arthur) as established in The Lantern Bearers.
The events of the novel follow and continue those of The Lantern Bearers. Artos (Sutcliff's version of Arthur) recalls his life as he lies near death, from the time when he served under his uncle, the British high king Ambrosius. He gathers a core cavalry group, Artos' Companions, who will be pivotal to the resistance of the British kingdoms to the invading Saxons. While visiting Arfon, in North Wales, where he grew up, Artos meets a woman, Ygerna, who drugs and seduces him. He is unaware that the woman is his half-sister, and that her seduction was a deliberate plan to gain revenge against their father; Ygerna is Uther's legitimate daughter, whereas Artos is Uther's illegitimate son. Artos' seduction and the conception of Medraut is Ygerna's means of bringing ruin to Artos.