Although the mortality rate was erratic, ranging from one fifth in some places to nine tenths or almost total elimination in others, the overall estimate of modern demographers has settled—for the area extending from India to Iceland—around the same figure expressed in Froissart’s casual words: “a third of the world died.” His estimate, the common one at the time, was not an inspired guess but a borrowing of St. John’s figure for mortality from plague in Revelation, the favorite guide to human affairs of the Middle Ages.
