Classicly

The Man Who Came Early is a science fiction short story by Danish-American author Poul Anderson. Similar in some respects to Mark Twain's A Connecticut Yankee in King Arthur's Court, the story is in fact its antithesis; Anderson sharply differs from Twain in his treatment of the "primitive" society in which the time traveller finds himself, and his assessment of a modern person's chances of survival in such a society.