I don't have, of course, to have the whole fallen empire thing. (Ireland, of course, had Dark Ages that one can rip off as well as England did.)
And that comment that a knight makes about those effete milksops who go through a ceremony to make a man a knight -- must show he can't just fight and so win it -- doesn't require such a civilization. (Or even one much different. People have funny notions about foreign customs.)
Still, besides the possibility of vistas and expanded world, there is the little matter that at one point, a character does something by magic that they didn't know was possible. Importing it to the kingdom of the story would explain it, and also add to the reaction of those learning how it was done.
