Epidemics accompany mankind as death follows life. AIDS, SARS, Ebola, and now Zika. The Spanish flu of 1918 may have killed up to 100 million people in the aftermath of World War One. Some are epochal, like the Black Death that arrived in the 14th century from the East. But predicting an epidemic or pandemic is unusually difficult because they are triggered by a random event: a pathogen crosses into humans from another species. The very same technological processes that contribute to accelerate the spread of these viruses—chiefly, the explosion of international travel—allows us to marshal the resources to fight them, which owe quite a bit to the renewed interest in medicine that followed the Black Death.