By the time Justinian's plague had run its course in AD 590, it had killed as many as 100 million people -- half the population of Europe -- brought trade to a near halt, destroyed an empire and, perhaps, brought on the Dark Ages. Some historians think that the carnage may also have sounded the death knell for slavery as the high demand for labor freed serfs from their chains. Justinian's plague was a "major cataclysm," says historian Lester K. Little, director of the American Academy in Rome, "but the amount of research that has been done by historians is really minimal."One quibble I have right now -- the population of Europe at that time probably wasn't anything like 200 million. The population of the whole Roman Empire at its peak was something in excess of 50 million, and that included north Africa, Anatolia, and the Levant.
Don't ever let work get in the way of the really important stuff.
Yeah, that "100 million deaths" figure seems like it was plucked out of thin air. I don't think that there is any way to know the population of the Mediterranean region with any degree of certainty during that period.