This book is the result of the combination of chance, curiosity, and a challenge. These three spurs to research were later augmented by a gradual realization on my part that its subject also presented an opportunity. The chance was this. Some years ago, an invitation came my way to attend a conference on the history of human rights and to prepare a talk on their place in the medieval ius commune, the amalgam of Roman and canon laws that dominated Eu ro pean legal education and infl uenced court practice from the Middle Ages through the Age of Enlightenment. I was then familiar in a general way with the concept of the law of nature, as every student of medieval law must be. I knew enough about it to think that it might help me prepare the talk. Natural rights and the place of morality in law have been strong, if contested, parts of the Western legal traditions for centuries, and the link between them and their public assertion in promoting the human rights of men and women enmeshed in Eu rope’s legal systems appeared to be a fruitful subject for investigation in preparing the talk. So it proved to be.