Q. What caused the plague? The learned doctors with whom I studied attributed the disease to a massive corruption of the air. In a report in 1348, these same scholars proved that this corruption began with a planetary conjunction of Saturn, Mars, and Jupiter on March 20, 1345. Some accounts spoke of cataclysms in the Orient, such as firestorms or rains of frogs, that spawned a drifting, disease-laden cloud. Clearly there is merit to these theories-only a contamination of the air could explain why some people were struck down in their homes, without having touched or even seen another victim. Most of the populace, however, believed the spiritual leaders who insisted that so great a disaster could only be God's punishment for the general wickedness of the age.