That past decade in particular has seen a drastic decline in the number of physical books being read, which in itself is quite a shame because reading a book off of a screen just does not have the same feel as an actual hardcover or paperback book in your hands. In the entirety of civilized human history, there have likely been millions of books written by hundreds of individuals, which deal with all kinds of fictional and nonfictional topics, like biology, religion, philosophy, history, economics, mythology and science. Leonardo Da Vinci is one of history’s greatest minds, and when he was alive, he wrote several books, some of which were fortunately able to survive the test of time. One of these books was his scientific journal known as the Codex Leicester (pictured), which is considered to be the most valuable and expensive book in the world, which is probably true considering that Bill Gates, the wealthiest man in the world, paid 30.8 million dollars for it.