Millions of people in Europe died from plague during the Black Death, though areas were not uniformly devastated by the epidemic.
The Black Death was an illness caused by bacteria (yersinia pestis) carried by fleas that lived on black rats. It caused fever, vomiting, coughing up blood, black pustules on the skin, and swollen lymph nodes. Then, 3 days later, often death.
In Florence, about 60% of people died of plague in 1648.
In 1348/9, plague came to Britain killing between 30-40% of the population. This is at a time when the population of Britain is estimated at 5-6 million people.
Frighteningly, it is estimated that up to two-thirds of the clergy of England died within a single year.
Milan, an Italian city-state, had a ruler, Visconti Luchino, a dictator who was able to stop almost all travellers into the city. Milan’s death rate was about 15 percent.
The 13th and 14th centuries in Europe had already been a time of great hardship. The climate had cooled, weather patterns were erratic, and crops often failed.
During the Great Famine of 1315–17, about 15% of the population of England and Wales died. Bodies found from this period are shorter and show signs of manuitrition. So, by the time the Black Death arrived, populations were already weakened.
However, weak and poor died alike. As chronicler Gilles Li Muisis wrote in France, where about half of the population died from plague, "neither the rich, the middling sort, nor the pauper was secure; each had to await God's will".