Epigraphs are like little appetizers to the great entrée of a story. They illuminate important aspects of the story, and they get us headed in the right direction.
Fate sits on these dark battlements, and frowns,
And, as the portals open to receive me,
Her voice, in sullen echoes through the courts,
Tells of a nameless deed.
Ann Radcliffe loves a good epigraph, but this one takes the cake for setting up reader expectations. We've got a personified Fate sitting on the "dark battlements" of Udolpho like a glorified gargoyle. We've got a disembodied voice echoing through the court, much like Du Pont's when Montoni is trying to have a conversation. And, of course, we've got the "nameless deed" that haunts us all the way through the book.
While Radcliffe has a fondness for shout-outs to other writers (James Thomson's a particular favorite), this little guy is all her own. And why not? There's no better way to foreshadow all the major events of Udolpho than by trotting out your very own epigraph.