Umberto Eco once said in an interview that sometimes, when he worked on a novel, he lived the story for years until he was done. That’s what he did with his second novel, Foucault’s Pendulum, which took him eight years to write.

It tells the story of three men who work for a vanity publisher. Tired of reading about grand occult conspiracies, they decide to invent their own, the grandest conspiracy yet, about the Knights Templars and their millennium-spanning plan for world domination.

They pool in elements from the Kabbalah, Gnostic cults, Rosicrucian and Freemasonic lore, Roman mysteries and Caribbean spiritualism and feed it into a computer, which they nickname Abulafia, after the famous Jewish mystic. Taking the random text fragments thrown up by the computer programme, they construct The Plan.

However, soon they’re convinced that it’s a real plan, and a secret society, just like the one they’ve invented, starts stalking them. When asked about Dan Brown’s debt to Foucault’s Pendulum for his The Da Vinci Code, Eco quipped, “(He) is a character from Foucault’s Pendulum! I invented him…I suspect Dan Brown might not even exist.”