Page "Black Death" Paragraph 14

Plague was reportedly first introduced to Europe at the trading city of Caffa in the Crimea in 1347.

After a protracted siege, during which the Mongol army under Jani Beg was suffering the disease, they catapulted the infected corpses over the city walls to infect the inhabitants.

The Genoese traders fled, taking the plague by ship into Sicily and the south of Europe, whence it spread north.

Whether or not this hypothesis is accurate, it is clear that several existing conditions such as war, famine, and weather contributed to the severity of the Black Death.