Causes of the Bubonic Plague

The Bubonic Plague's first appearance in medieval Europe from 1348-1351, and it was terrifying. At least one-quarter to one-third of the population died in those few years; entire villages were depopulated, and no country was untouched.

King Philip VI of France asked the University of Paris to determine the cause. Forty-nine members of the medical staff studied the matter and wrote the Paris Concilium.

They produced more than one theory of why humans were suffering from it, while maintaining that the plague was too mysterious for human beings to ever truly understand the origin. They drew from the available authorities: Avicenna's work on pestilential fever, Aristotle's Meteorology on weather phenomena and putrefaction, Hippocrates' Epidemics on astrology in medicine.

Their theories:

—The Concilium followed Aristotle's idea that a conjunction of Jupiter and Saturn was disastrous. Albertus Magnus believed a conjunction of Jupiter and Mars would bring plague. A conjunction of Saturn, Jupiter, and Mars took place in 1345 right after solar and lunar eclipses, under the sign of Aquarius, compounding the disastrous effects of the planets. Jupiter was sanguine, hot and wet—the worst combination that would lead to putrefaction.

—Another possible cause was poisonous gases released during earthquakes. Disadvantageous conjunctions of constellations produced winds that distributed gases rising from rotting carcasses in swamps. The poisonous vapors would be inhaled and go straight to the heart (they thought the heart was the organ of respiration), and then cause the body's vital organs to rot from the inside.

—There was also the possibility of God's punishment for man's wickedness.

Of course, there was no reason to believe that these causes were mutually exclusive.

The plague was devastating, and also didn't end in 1351. It remained endemic to Europe, as I'll discuss next time.