But just how accurate is De’ Mussi’s account? The basic narrative, that the Mongols used Plague cadavers as a weapon is likely true. The idea of throwing diseased corpses into enemy cities is an old one. And it is consistent with the ideas prevalent at the time about how disease spread.

So the idea that a Mongol commander, angry about having been forced to lift his siege of a city, might fling the corpses of Plague victims into that city to kill the inhabitants is completely plausible. Furthermore, it was technically achievable given Mongol siege technology.

And De’ Mussi’s suggestion that the Mongol’s act of biological warfare at Caffa lead to the Plague that killed millions of people is often repeated as fact. However, the truth is likely a bit different. We know that the Black Death entered Western Europe from Crimean trading ports. However, there’s no reason to tie the biological attack at Caffa with the introduction of the disease.

Mongols controlled many ports in the Crimea region and infection rapidly spread through all of them. Plague-carrying rats could easily have entered Italy on ships from any of these ports. While diseased sailors from Caffa may have helped spread the Plague into Italian ports, they were likely not the only or even the first to do so.

Regardless of just how the Plague spread to Western Europe, the results were devastating and transformative for the course of European history. In cities across the continent, people died in staggering numbers. The cramped conditions and poor sanitation in Medieval cities allowed the disease to spread rapidly. And the sudden mortality was so great as to seem apocalyptic to contemporary observers. All across Europe, people were convinced that the world was ending. Of course, the world did not end, but it did change.

Prior to the Black Death, Europe struggled with overpopulation, which depressed wages for peasants and created conditions that allowed serfdom to flourish. When huge numbers of people died, those who survived found that they could command much higher prices for their work. And the sudden availability of farmable land allowed Medieval peasants to leave their hereditary estates and seek better conditions elsewhere.

Europe changed culturally as well during the Black Death. The constant presence of mortality served as a reminder of the great leveler of death. Artists began incorporating this theme into their works to remind their audience that rich or poor, priest or peasant, all must die.

In many ways, these changes paved the way for the social unrest and transformation that followed. Restrictive laws enforcing serfdom on the newly mobile peasants led to massive insurrections in Western Europe. And the influence of the Black Death echoed across the following centuries and helped to lay the foundation for the massive social changes that followed.

And whether or not the Mongols helped to introduce it to Europe with an act of biological warfare, it reminds us just how devastating a weapon it can be.