Resistance to the abuse of monarchical power in the twelfth and thirteenth centuries was based on assumptions which permeated the society of western Europe. Magna Carta was more than a simple reaction against Angevin government, and more than a statement of the privileges which the Angevins had made available; it was also a statement of principles about the organization of a feudal state. As such it drew on a common body of experience and custom which, with local variants, was shared throughout western Europe and the Latin states in the east. Hence the Norman and Angevin kings had to contend with men who shared strong views on the constitution of society, on title to feudal property, on the right to judgement and on the proper conduct of lords and kings. The Angevins gave their men the grievances and the education in government which were woven into the tapestry of Magna Carta. But the warp and weft were derived from the structure of society itself.

This common experience was embodied in custumals and law-books, it was formulated in statutes, it was sharpened by the conflict between Church and State, it was laid down as assizes when new states were founded, and it was stated in charters of liberties when the interaction of royal policy and aristocratic interests exploded into political crises. Together these scattered and widely different sources reveal legal and political principles of remarkable permanence and pervasiveness. For example, the insistence on judgement by peers in cap. 39 of Magna Carta was simply an assertion of a generally recognized axiom. It received its first clear statement in the edict of the Emperor Conrad II of 1037 which laid down that military tenants were not to be deprived of their fiefs ‘except by the laws of our ancestors and the judgement of their peers’.