An ancient philosophy is becoming popular again thanks to author Ryan Holiday.
These are some of the strangest, most mysterious books ever written.
Books teach us, inform us, amuse us and provoke us. But some books plainly befuddle us. They invoke mysteries that hint of something ancient, extraterrestrial or possibly divine. Here are 5 such books: the Voynich Manuscript, Codex Seraphinus, Rohonc Codex, the Smithfield Decretals and the Book of Soyga.