Justinian’s Plague was “a pandemic that killed as many as 100 million people around the world during a 50-year period in the 6th century A.D.”
It spread through Europe as far north as Denmark and as far west as Ireland… The plague swept across the Mediterranean during the reign of Byzantine Emperor Justinian I in the early 540s and according to some historians changed the course of European history because the empire then entered a period of decline.
Carried by rats and parasites, the disease spread rapidly because families at the time lived in close quarters in poor hygienic conditions…
Modern scholars believe that the plague killed up to 5,000 people per day in Constantinople … and later went on to destroy up to a quarter of the human population of the eastern Mediterranean.
Hat tip: Rogue Classicism.