Eco is having the last laugh.
In Foucault’s Pendulum Umberto Eco is writing a huge joke with the whole world as the punchline. He takes everything you know about history (and quite a few things you don’t) and wraps them all up in such a way that they make sense. Or better yet, in a brilliant act of post modernism, he has his characters do it. Causabon, the narrator of the tale, spends his time explaining to the reader that none of this is real. And yet, when you put the book down, all the connections which have been explained become glaringly obvious in real life. It’s like when you buy a new car and suddenly all you see on the road is that model. Eco creates the pathways for your own brain to make the connections. I realize this tells you nothing about the plot of the book, but that’s half the fun of reading it. You have to decide for yourself where he’s being serious and where he’s playing a joke. And even after you decide…you’re probably wrong.
Like Tim Powers, Eco is very skillful at weaving historical fact into a fantastic tale. Ultimately, you don’t know if he’s pulling your leg or if he’s just written down a long forgotten history and is downplaying it as fiction to make sure he doesn’t get into trouble with the powers that be.