The Black Death, Part I
Philip Ziegler describes how, in the mid-fourteenth century, about one third of the population of Western Europe perished from bubonic plague.
It is now established beyond doubt that the Black Death which ravaged Asia, Africa and Europe in the mid-fourteenth century was a particularly virulent epidemic of bubonic plague. There remains, indeed, little mystery about its origins, nature and course. The cradle of the disease has been identified with fair certainty as Lake Issyk-Koul in what is now Russian Central Asia.
Some natural calamity, probably a flood, drove the tarbagans, susliks and other rodents from their homes around the lake. With them travelled fleas whose blood was infected with the plague bacillus, Pasteurella Pestis. Once the flea was on the move, the black rat took up the task of porterage.
Along the trade routes flowed the disease, arriving, sometime in 1346, at Caffa, now Feodosia, a Genoese trading station in the Crimea. From there, and probably from other similar ports, the galleys bore the Black Death to Europe.