Books that introduce too many characters all at once: how do you deal with it?

I'm reading at the moment {{The Winter King by Bernard Cornwell}}, which covers Britain / Saxon era, Arthurian legends, and the like.

I am fond of the setting and the topic. However there are so many different characters — making it hard to follow. I'll give the editor credit, though: they have at the beginning a list of all characters and places, a bit like in a play. But we're talking ~50 names of people, and a dozen or more names of places…

Have any of you had similar experiences with this book, or other books? At what point do you give up? My rule of thumb is giving a novel "a hundred pages of grace"…