Some Theories of How the Black Death Devastated the Medieval World


By Dorsey Armstrong, Ph.D.Purdue University

When the Black Death devastated the medieval world in the middle of the 14th century, people were by turns resigned, repentant, hedonistic, and terrified—sometimes experiencing each of these responses in quick succession or almost simultaneously. However, there was a desperate desire to understand where this thing had come from and what could be done to stop it.

Building of the University of Paris.
The University of Paris made efforts to explain what was going on with the plague at the time. (Image: V_E/Shutterstock)

The Medieval World Didn’t Have Much to Work With

The greatest minds of the day turned their attention to questions about the plague, and in the years immediately following the first outbreak in the West in 1347, dozens of plague treatises were composed and circulated. 

As might be guessed, however, at a time when the theory of germ transmission did not yet exist and there were no antibiotics, there was little written that was of any real help.

But looking at these medical and scientific theories offers a fascinating window into the medieval world—not just regarding the plague outbreak, but in terms of how certain fields of knowledge were understood and valued, and how the medieval mind saw connections and parallels between individual people, humanity at large, and the whole cosmos.

This is a transcript from the video series The Black Death: The World’s Most Devastating PlagueWatch it now, on Wondrium.

The University of Paris Really Tried

The most authoritative commentary on the plague came from the medical faculty at the University of Paris, who were charged by the French king, Philip VI, with coming up with an explanation for the crisis that was confronting medieval society. 

The text is quite long, and it has two parts. In the first section, the medical faculty offered three chapters that detailed the causes of the plague. In part two, they spent seven chapters offering suggestions for remedies or steps one might take in the hope of having some effect on the plague.

They started their tract in the way that innumerable college students had been taught to start their essays—they begin with the general, and then get a little more specific: “We say that the distant and first cause of this pestilence was and is the configuration of the heavens.”

Learn more about cultural reactions from flagellation to hedonism.

Did the Planets Have Something to Do With It?

They noted that on March 20th, 1345, there was a conjunction of three planets in Aquarius—Mars, Jupiter, and Saturn—and this conjunction somehow caused “a deadly corruption of the air around us”. 

Image of the night sky with two glowing dots in the sky.
The conjunction of planets was believed to have had something to do with the Black Death. (Image: Viktar Malyshchyts/Shutterstock)

They cited no less an authority than Aristotle, plus earlier medieval philosophers such as Albertus Magnus, who had argued that the conjunction of Mars and Jupiter causes a great pestilence in the air, especially when they come together in a hot, wet sign. 

For Jupiter, being wet and hot, draws up evil vapors from the Earth and Mars, because it is immoderately hot and dry, then ignites the vapors, and as a result, there are lightning, sparks, noxious vapors, and fires throughout the air.

They go on to say that the effects of this were only intensified because Mars was in the sign of Leo just before the key period in question.

Besides the medical faculty at the University of Paris, plenty of other great minds of the day weighed in on the astrological causes of the plague. Oxford scholar Geoffrey de Meaux wrote his own plague treatise on the conjunction of the planets in 1345.

Learn more about medieval theories about the Black Death.

More Medieval Minds at Work

Geoffrey de Meaux said the Paris medical faculty was wrong to focus on Jupiter as being a contributor—it’s really Mars and Saturn that people should be worried about, he said. Geoffrey went on also to assert that eclipses played a role in the current outbreak.

Silhouette of an astronomy telescope with the twilight sky.
When the minds of the Middle Ages didn’t have answers, they looked to the skies for answers. (Image: AstroStar/Shutterstock)

Once again, 1345 is the key year. It has been and is known by all astrologers that in the year 1345 there was a total eclipse of the Moon, of long duration, on 18 March. At the longitude of Oxford, it began an hour after the Moon rose.

At that time the two planets were in conjunction with Aquarius, and Mars was with them in the same sign, within the light of Jupiter.

He went on to explain that when the Sun is directly opposite the Moon, as occurs in a total eclipse, then the power of each of them reaches the Earth in a straight line, and the mingling of the influence of Sun and the Moon with that of the superior planets creates a single celestial force which operates in conformity with the nature of the superior planets, which have drawn to themselves the powers of the Sun and Moon.

He observed that, on their own, the Sun, Moon, and planets would have minimal impact on the world—but when all their energies are combined and aligned, well, the Earth is in trouble.

So activity in the heavens—whether it be planetary alignment, eclipses, certain planets being in certain quadrants of the sky—was regarded by multiple great minds of the day as the ultimate cause and source of the plague.

Common Questions about Some Theories of How the Black Death Devastated the Medieval World

Q: How did the medical faculty of the University of Paris approach the Black Death?

After the Black Death struck the medieval world, they were ordered to find out why this was happening and so they wrote a long text made up of two parts, the first explaining the cause of the Black Death and the second trying to propose remedies and cures for it.

Q: How did the medical faculty of the University of Paris view the plague?

The medical faculty of the University of Paris argued that the plague had something to do with the conjunction of planets. Specifically, Mars, Jupiter, and Saturn, which somehow led to a “corruption of the air”.

Q: What did Geoffrey de Meaux and the University of Paris disagree about?

Like many minds in the medieval world, they both believed the Black Death had something to do with the conjunction of the planets, but Geoffrey de Meaux thought the University of Paris was wrong to focus on Jupiter as a contributor because he thought they should actually focus on Mars and Saturn.

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