The victims of the Black Death sought an explanation for the terrible disease visited upon them. They had reason to hope that the explanation could be found. In recent times, scientific inquiry had flourished. The first universities of Europe were founded during the twelfth century. Lecturers at these universities questioned many of the doctrines of the church, which remained the dominant institution in society. Christianity was their faith—but their quest was to learn how the Christian God had created and ordered the natural world. While ordinary people looked to the Bible and their faith for the answer to the unstoppable pestilence, doctors and scientists could not agree on the true cause. Some explained it as an astronomical event, noting that the planets had recently entered an unlucky alignment in the heavens. Others blamed miasmic vapors belched up from underneath...