Perhaps superstition caused the Muslim Tartars to blame their misfortune on the Christian Genoese. Or perhaps a Christian and Muslim had become involved in a street brawl in Caffa, and the Tartars wanted revenge. In any case, the Tartars sent an army to attack Caffa, where the Genoese had fortified themselves. As the Tartars laid siege to Caffa, plague struck their army and many died. The Tartars decided to share their suffering with the Genoese. They used huge catapults to lob the infected corpses of plague victims over the walls of Caffa. As the Tartars had intended, the rotting corpses littered the streets, and the plague quickly spread throughout the besieged city. The Genoese decided they must flee; they boarded their galleys and set sail for Italy, carrying rats, fleas, and the Black Death with them” (Corzine, 1997).
The plague traveled on trade routes and caravans. Its path of death was generally from south to north and east to west, passing through Italy, France, England, Germany, Denmark, Sweden, Poland, Finland, and eventually reaching Greenland.