What did medieval people make of this epidemic? In their view, what caused it? For most of those who thought about that question, divine wrath pro-vided the most satisfactory general answer. Other causes were often cited, but for most writers such other reasons were “secondary,” explaining how plague came in a particular time or place. Only God’s wrath could explain such a com- prehensive disaster. Furthermore, God’s anger did not in this case fall on partic-ular sinners, as was the case with leprosy. The scale of the plague suggested rather that the whole civilization, or the whole human race, was being punished.The general social and economic hardships of the previous hundred years gave such arguments credence: man had sinned, the judgment of God was at hand. Millenarian expectations were close to the surface already; they had emerged in Italy around 1260, and the great epidemic would call them forth again.
Within the general framework of a heaven-sent scourge, medieval thinkers offered a number of more immediate causes, and on the basis of those causes proposed (or put into effect) some remedies. At the head of the list of such imme-diate causes was “bad air,” the official doctrine of the medical faculties of some universities, where it was integrated with Galenic theory. Hot, moist air, putri-fied (ultimately by God’s action, to be sure), entered the lungs and caused a blood disorder. Plague resulted. But if widespread agreement existed on the role of bad air, great disagreement ensued about the source of that air. Some found its origins in the heavens; thus the Sorbonne cited an unfortunate conjunction of the planets that engendered bad air. Eclipses, always regarded as grave astronomical events, were another possibility. Comets—sublunary phenomena in the dominant Ptolemaic astronomy— were likely disturbers of sublunary air. For some the moon influenced the stages of the plague, as it seemed to affect other periodic human physical events such as menstruation. Others maintained that “plutonic,” not astronomical, forces produced bad air: corruption poured from openings in the earth such as volcanoes. Sicily, with both Mount Etna and early cases of plague, was especially suspect. Or perhaps the bad air merely accompanied a variety of natural cataclysms; the Sorbonne instanced earth-quakes as “provoking an unaccountable abundance of frogs and reptiles.”10 Bad air as well as frogs might result from such disturbances.