There are many reasons why a number can become special. These reasons are often connected to important, albeit random, events in our lives. This was the case for this book’s author and his favourite number. In the assorted domains of football, comic strips, classical and rock music, science and fantasy, the number nine evokes something magical, heroic, fascinating, or sublime: the exploits of a centre forward, a Beethoven symphony, a Beatles song, the rings of power created by a dark Lord, the worlds of Norse mythology, and space stations at the edge of the universe. The number nine has become the symbol of a wide variety of things that are crucial to our culture, and accordingly it evokes facts, experiences, and behaviour. To find out how this is possible, readers can immerse themselves in the stories told in this book, which sometimes digs into the past, but always with the future in mind.

Marco Ciardi teaches History of Science at the University of Florence.