This was probably one of the hardest and best books I've ever read. A deliberately ahistorical historical novel, it tells the story of two men, one an astronomer, the other a surveyor, about whom very little is actually known, in the form of a picaresque tale that tells a story within a story, with some digressions into even deeper layers of narrative. All sorts of absurd episodes about talking dogs, flying magicians and the hollow earth are interwoven. Nevertheless, you learn a lot about history, including historiography and how much you can trust it, but also about colonial America, slavery, astronomy, seafaring and much more, and of course about the surveying of the Mason-Dixon line, which was an engineering achievement at the time and is still regarded as the dividing line between the northern and southern states of the United States. The novel is at times terribly funny and at other times equally tragic, with occasional detours into the absurd. Because of the very sophisticated style, with eighteenth-century vocabulary and spelling, you should have a dictionary and an encyclopaedia handy, but then it's great fun. I'm looking forward to reading it again some day.