The Bubonic Plague, more commonly known as the Black Death was the disease responsible (possibly in conjunction with other diseases, such as the pneumonic plague) for the greatest epidemic of all time. It is important to know that it was not the epidemic with the greatest number of deaths (some recent epidemics have killed as many as 25 million people, which is greater than the entire population of Europe at the time of the Black Death) but rather that it killed the greatest percentage of the population; a staggering one third of the population of Europe died in the span of five years.
Though some cases of the plague were seen as early as the 6th century, the well-known epidemic began in the Gobi desert in the 1320s, for reasons that are still unknown. Borne by rats and transmitted by the fleas that infested them, the Black Death quickly swept across the continent, reaching Italy in 1347.
The plague was exceptionally lethal, killing its victim in three or four days with no chance of recovery. It began with a headache and shivers, at which point the victim knew he was doomed. Within a day, his lymphatic glands would swell up and turn black, easily visible through the skin. He would then begin to vomit blood almost continuously for up to another day or two, then die.
The people were hysteric, and understandably so; from the first occurrence of the disease in Florence, it only took six months for a third of the population to die and within a year, between 45% and 75% were dead. This was a particularly severe case, but every city was struck, and most fared little better than Florence. Unable to explain these occurrences, some people began assuming that this was a punishment from God and attempted to atone for the sins of the world; others blamed the Jews, accusing them of witchcraft and poisoning the water, and slaughtering them mercilessly for these imagined evils. The church attempted to stop both of these practices, but to no avail. City councils also tried to contain the damage, but the people were mad with fear and chaos reigned supreme.
The plague also influenced the art of the time, which became incredibly morbid. A new style emerged, that of the "danse macabre." Paintings of this sort were fairly conventional scenes of city life of daily activities, but many characters in them were replaced with skeletons. The dead walked among the living, a metaphor for what was happening in the world at the time.
Eventually the epidemic abated slightly, though several smaller epidemics occurred over the centuries to come and some European countries had still not regained their pre-plague population even by the 17th century.