Plague symptoms were first described in 1331 in southwestern China, then part of the Mongol Empire. Plague-infested rats accompanied Mongol armies and merchant caravans carrying silk, spices, and gold across Central Asia in the 1330s. The rats then stowed away on ships, carrying the disease to the ports of the Black Sea by the 1340s.

In October 1347, Genoese ships brought the plague from Kaffa to Messina, from which it spread across Sicily. Venice and Genoa were hit in January 1348, and from the port of Pisa the disease spread south to Rome and east to Florence and all of Tuscany. By late spring, southern Germany was attacked. Frightened French authorities chased a galley bearing plague victims away from the port of Marseilles but not before plague had infected the city, from which it spread to southern France and Spain. In June 1348, two ships entered the Bristol Channel and introduced it into England, and from there it traveled northeast into Scandinavia. The plague seems to have entered Poland through the Baltic seaports and spread eastward from there (Map 11.1).

Medieval urban conditions were ideal for the spread of disease. Narrow streets were filled with refuse, human excrement, and dead animals. Houses whose upper stories projected over the lower ones blocked light and air. In addition, people were already weakened by famine, standards of personal hygiene remained frightfully low, and the urban populace was crowded together. Fleas and body lice were universal afflictions: everyone from peasants to archbishops had them. One more bite did not cause much alarm, and the association among rats, fleas, and the plague was unknown. Mortality rates can be only educated guesses because population figures for the period before the arrival of the plague do not exist for most countries and cities. Of a total English population of perhaps 4.2 million, probably 1.4 million died of the Black Death. Densely populated Italian cities endured incredible losses. Florence lost between one-half and two-thirds of its population when the plague visited in 1348. The most widely accepted estimate for western Europe and the Mediterranean is that the plague killed about one-third of the population in the first wave of infection.

Nor did central and eastern Europe escape the ravages of the disease. As the Black Death took its toll on the Holy Roman Empire, waves of emigrants fled to Poland, Bohemia, and Hungary, taking the plague with them. In the Byzantine Empire, the plague ravaged the population.

Across Europe, the Black Death recurred intermittently from the 1360s to 1400. It reappeared from time to time over the following centuries as well, though never with the same virulence because by then Europeans now had some resistance. Improved standards of hygiene and strictly enforced quarantine measures also lessened the plague’s toll. Only in 1721 did it make its last appearance in Europe, in the French port of Marseilles.