In a striking passage near the beginning of his contribution to the Penguin History of the Church, R.W. Southern writes:

The identification of the church with the whole of organized society is the fundamental feature which distinguishes the Middle Ages from earlier and later periods of history. At its widest limits it is a feature of European history from the fourth to the eighteenth century—from Constantine to Voltaire. In theory, during the whole of this period only orthodox and obedient believers could enjoy the full rights of citizenship. … Just as...