This book tells the story of the formation of a new field of knowledge. It shows how various authors combined their knowledge, experience, and critical thought to write lawbooks that made various disparate customs into a field of knowledge known as customary law. These authors wrote texts, known as the coutumiers in the French legal tradition, in thirteenth-century northern France. ‘Customary law’ typically refers to a type of rule made in practice, and in the courts, by the community, which can include ‘the people’ in some form, lords and kings, or lawyers and judges. Customs concerning specific rules of property, succession, and other subjects certainly emerged out of this oral practice. Coutumier authors, however, successfully crafted customary law into an expository genre of writing, one that took ideas of custom from practical experience and different forms of book learning and transformed them into bodies of customary law.

This chapter argues that the empire of Genghis Khan made 'Asia' and/or 'the East'. Genghis Khan not only politically unified most of Asia in the thirteenth century but also changed the conception of sovereignty throughout the continent by disseminating, through his own example, the norm of the political ruler as the exclusive supreme authority, legitimised by world domination. This chapter gives an overview of the rise and decline of the Chinggisid world order (as constructed by the Mongol world empire and later maintained by the successor khanates: Yuan, Chaggataid, Ilkhanate, Jochid/Golden Horde). At its peak this world order covered most of Asia, from present-day China in the East to present-day Russia in the North and the present-day Middle East in the West. However, even the areas offically out of the reach of the Mongols (e.g. the Indian subcontinent) were very much influenced by them. This chapter also introduces institutions associated with the Chinggissid sovereignty norm – such as tanistry and astronomy/astrology – that will be traced to subsequent world orders. It also speculates about the possible causes for the decline of this world order, including the plague.