The tale of one thousand three hundred and forty-eight when in the illustrious city of Florence, the fairest of all the cities of Italy, there made its appearance that deadly pestilence, which, whether disseminated by the influence of the celestial bodies, or sent upon us mortals by God in His just wrath by way of retribution for our iniquities . . ." —The Decameron by Giovanni Boccaccio

What event is Boccaccio referring to in this excerpt?
A.
the Mongolian invasion
B.
the Bubonic Plague
C.
the Crusades