The Rule of Four by Ian Caldwell and Dustin Thomason is a runaway international bestseller, topping the charts on both sides of the Atlantic.But the foundation of The Rule of Four, as all its readers know, is a little-known text from the fifteenth century, the Hypnerotomachia Poliphili.Lurid, dreamlike, extremely erotic and written in many different languages and codes, the exact meaning of the Hypnerotomachia has eluded scholars for centuries.