How did people of the medieval period explain physical phenomena, such as eclipses or the distribution of land and water on the globe? What creatures did they think they might encounter: angels, devils, witches, dogheaded people?

This fascinating book explores the ways in which medieval people categorized the world, concentrating on the division between the natural and the supernatural and showing how the idea of the supernatural came to be invented in the Middle Ages.

Robert Bartlett examines how theologians and others sought to draw lines between the natural, the miraculous, the marvelous and the monstrous, and the many conceptual problems they encountered as they did so. The final chapter explores the extraordinary thought-world of Roger Bacon as a case study exemplifying these issues. By recovering the mentalities of medieval writers and thinkers the book raises the critical question of how we deal with beliefs we no longer share.

To begin with, consider the following quotation from the preface to Serendipities (my
italics):
In other words, I feel that what links the essays collected here is that they are about
ideas, projects, beliefs that exist in a twilight zone between common sense and lunacy, truth and
error, visionary intelligence and what now seems to us stupidity, though it was not stupid in its day
and we must therefore reconsider it with great respect.2