Having originated in China and Inner Asia, the Black Death decimated the army of the Kipchak khan Janibeg while he was besieging the Genoese trading port of Kaffa (now Feodosiya) in Crimea (1347). With his forces disintegrating, Janibeg used trebuchets to catapult plague-infested corpses into the town in an effort to infect his enemies. From Kaffa, Genoese ships carried the epidemic westward to Mediterranean ports, whence it spread inland, affecting Sicily (1347); North Africa, mainland Italy, Spain, and France (1348); and Austria, Hungary, Switzerland, Germany, and the Low Countries (1349). A ship from Calais carried the plague to Melcombe Regis, Dorset, in August 1348. It reached Bristol almost immediately and spread rapidly throughout the southwestern counties of England. London suffered most violently between February and May 1349, East Anglia and Yorkshire during that summer. The Black Death reached the extreme north of England, Scotland, Scandinavia, and the Baltic countries in 1350.
There were recurrences of the plague in 1361–63, 1369–71, 1374–75, 1390, and 1400. Modern research has suggested that, over that period of time, plague was introduced into Europe multiple times, coming along trade routes in waves from Central Asia as a result of climate fluctuations that affected populations of rodents infested with plague-carrying fleas.
The rate of mortality from the Black Death varied from place to place: whereas some districts, such as the duchy of Milan, Flanders, and Béarn, seem to have escaped comparatively lightly, others, such as Tuscany, Aragon, Catalonia, and Languedoc, were very hard-hit. Towns, where the danger of contagion was greater, were more affected than the countryside, and within the towns the monastic communities provided the highest incidence of victims. Even the great and powerful, who were more capable of flight, were struck down: among royalty, Eleanor, queen of Peter IV of Aragon, and King Alfonso XI of Castile succumbed, and Joan, daughter of the English king Edward III, died at Bordeaux on the way to her wedding with Alfonso’s son. Canterbury lost two successive archbishops, John de Stratford and Thomas Bradwardine; Petrarch lost not only Laura, who inspired so many of his poems, but also his patron, Giovanni Cardinal Colonna. The papal court at Avignon was reduced by one-fourth. Whole communities and families were sometimes annihilated.