The pandemic of the mid-1300s was actually a deadly stew of three related diseases—bubonic plague, septicaemic plague and pneumonic plague, which infected the lungs, according to historian Norman Davies. “The result,” writes Davies in Europe, A History, “was mass mortality.” At the height of the plague, 800 people died each day in Paris, 500 in Pisa and 600 in Vienna. Half of Siena died within a single year, as did 50,000 of Florence’s 100,000 citizens. Giovanni Boccaccio’s Decameron, a classic of western literature, contains 100 stories told by 10 people sheltering from the plague. “One man shunned another,” Boccaccio explained, and father and mothers “were found to abandon their own children to their fate, untended, unvisited as if they had been strangers.”