Oswald Spengler's 'The Decline of the West'. The primary thesis of the author is of a cyclical development and decline of civilization (and his estimate that western civilization in particular is in the declining phase, hence perhaps the not so apt title to modern eyes). More importantly though Spengler's breadth of knowledge and culture (across science, philosophy, architecture, fine-arts, jurisprudence, literature) is just staggering and way beyond that of his contemporaries or present-day-authors.