Epidemiologists—the scientists who track the incidence and spread of diseases—are always on the lookout for the next big outbreak. But predicting the future is tricky. So, to better understand how epidemics get started and how to counteract them, they often study examples from the past. Deadly diseases have been literally plaguing humanity for as long as we’ve existed, so there’s a lot of material to work with—if you can piece together what happened. And sometimes, they can, even for outbreaks that occurred hundreds or thousands of years ago. So today, we’re going to talk about 6 of human history’s most fascinating – and terrifying – ancient outbreaks.