All you need for a plague to go pandemic are population clusters and travelers spreading the bacterial or viral pathogens. Many prehistoric civilizations died fast, leaving cities undamaged to mystify archeologists. Plague in Athens killed 30% of the population 430-426 BCE. When Roman Emperor Justinian I caught bubonic plague in 541 CE, contemporary historian Procopius described his symptoms: fever, delirium and buboes - large black swellings of the...