It is important to bear in mind that the conception of the universal church and empire was not regarded simply as an idea which the philosopher and the publicist wrote and disputed about, but as manifest in facts, which every eye could see and every mind realize. There actually existed an empire, an imperial crown and coronation; there actually existed a Holy See and a ministering priesthood. And the authority of the rulers of the universal state was not simply vague and theoretical; it was discernible in crusades, in pilgrimages, in the ‘Truce of God.’ Men realized themselves no doubt in an ever increasing degree through the Middle Ages, national characteristics becoming more and more pronounced, as Englishmen, Frenchmen or Spaniards; but they also thought of themselves quite naturally as members together of the common society of Christendom.[1] If we comprehend the _oneness_ of human society in the Middle Ages, as actively believed in by the average thinking man and unquestioningly accepted as a patent fact by the average uneducated man, we can realize what is meant by the phrase ‘ages of faith’ and at the same time avoid some of the pitfalls that lie in the path of any one seeking to study the exceptions to the rule, namely, the heresies of these ages of faith. What were the conditions that generated heresy? First, there were psychological conditions. In contrast to the bustling and multiform activity of the modern world the Middle Ages may at a first glance give an impression of inactivity and sameness. Such an impression, if it is encouraged by the intellectual dormancy of the ninth and tenth and, in some degree, of the eleventh centuries, is completely at variance with the facts of the twelfth and thirteenth centuries, in which the mind of Western Christendom was very much awake indeed. The impression also ignores what is one of the most marked characteristics of mediæval history as a whole—the clash and conflict and the dissonances of it. While the idea of the universal empire still held sway, secular princes, pursuing purely separatist ambitions, made war one upon another and the nations of Europe were in the throes of parturition. Typical of the incongruities of mediæval life was the glaring contrast between the glorious minster and the mean and filthy hovels round it to be seen in every city; but that there was incongruity in spending immense wealth, time and labour on building a house for God to dwell in, while housing themselves in dwellings rude and insanitary was not apparent to the occupants. There was another incongruity inside the churches themselves. Together with images that were sacred and beautiful there were hideous gargoyles, grotesque figures, whose inspiration was not Christian but pagan. Congregated together were saints and satyrs, and Pan is found in company with Christ. Art was made the handmaiden of religion: that did not mean that she was wholly consecrated. St. Bernard complained that the eyes of monks as they