I. THE CHANGING CLIMATE OF OPINION
We cannot say that the Middle Ages ended with the thirteenth century—or with the sixteenth. Medieval civilization was full of vigor; it did not yield quickly or easily to new beliefs or new forms of organization. In one sense it never died, since many medieval ideas and institutions were slowly adapted to meet new conditions and survived well into the modern period. It is true, however, that from the end of the thirteenth century on, the climate of opinion became less favorable to medieval ways of thinking and acting. This change in the intellectual climate was like a change in the physical climate; it did not happen suddenly and the general trend was interrupted by temporary reversals. Medieval civilization declined through a long autumn period—an autumn which had its bright, sunny days as well as its frosts and rains. And the winter which followed the medieval autumn was short, and relatively mild, not like the terrible Fenris-winter which came at the end of the ancient world. The new climate was not entirely unlike the old; there was more continuity between late medieval and early modern civilization than between the civilization of the Roman Empire and that of the eighth century.
There is no doubt that the beginning of the change in the climate of opinion came in the last quarter of the thirteenth century. For once all the indices agree—there was a sharp break in politics and in economics, in thought and in the arts. Young men who witnessed the defeat of Manfred and the pious death of the crusading St. Louis were hardly more than middle-aged when Manfred's grandson reconquered Sicily from the papal champion, and St. Louis’ grandson attacked a pope. Scholars who listened to the last lectures of Thomas Aquinas lived to hear his basic belief in the unity of all knowledge assailed. Sculptors who worked
