The Number One Best-Selling Book Ever

Euclid is one of my favorite people ever to have lived we don't know if he lived. He wrote a book called the Elements which I'll let you guess how popular was this book top in terms of the number of people who have read this book ever. Mao's little red book  was basically the standard math textbook for at least two millennia or something it was a standard math textbook among everyone in the Christian slash Muslim world. The biggest secular book ever it's got the biggest readership in history and that is secular because if you consider Mao's red book to be not essentially religious by another name so that is extraordinary.