The relationship between the Mongols and the Genoese was often testy. The city functioned as a major source of the slave trade to the Turkish Sultanates in Anatolia and the Mamlukes in Egypt. The Khan of the Golden Horde, Toqtai, apparently took exception to the enslavement of his subjects and besieged the town of Caffa in 1307. Ultimately, this siege ended in the city being burned to the ground and the Genoese expelled. Relations remained strained until the death of Toqtai.
The new Khan, Özbeg, welcomed the Genoese back and even ceded them land to expand the settlement. By the 1340s, Caffa was once again a thriving port. However, this peaceful coexistence between the Genoese and the Mongols didn’t last very long. Soon, there were disputes between the two parties that lead to violence.
In response, the new Khan, Janibeg, launched another siege of the city that was ultimately broken by an Italian relief army that killed thousands of Mongols and destroyed their siege engines in a pitched battle.
But the Mongols soon raised another army and returned to lay siege to the city again. This time, the Mongols faced a far more dangerous enemy than the Italians: plague. The Black Death began to spread rapidly among the Mongols through the cramped conditions of the siege camps. As the Mongol besiegers began to fall to the disease, the balance of power shifted back towards the Genoese.
Secure in their fortified city and regularly resupplied by Italian ships, the citizens of Caffa simply had to wait for the Plague to run its course through the Mongol ranks.
Janibeg was in a far worse position. His army was dwindling and the chance of taking the city was becoming increasingly remote. Finally, Janibeg decided that Caffa wasn’t worth the cost and ordered the siege lifted. But before leaving, Janibeg ordered the bodies of those who died of plague gathered up.
Then he ordered them flung over the ramparts of the city in the hope that the people inside would contract the disease. The plan worked and within a few weeks, the Plague was spreading rapidly inside the city of Caffa. But this was just the first taste Europeans had of what was to come.
According to an Italian notary, Gabriele de’ Mussi, who reported the events at Caffa for posterity, “among those who escaped from Caffa by boat were a few sailors who had been infected with the poisonous disease. Some boats were bound for Genoa, others went to Venice and to other Christian areas.
When the sailors reached these places and mixed with the people there, it was as if they had brought evil spirits with them: every city, every settlement, every place was poisoned by the contagious pestilence.” De’ Mussi’s account of events implies that the siege of Caffa may have been the origin point for the Plague’s introduction into Europe.