All you need for a plague to go pandemic are population clusters and travellers spreading the bacterial or viral pathogens. Many prehistoric civilisations 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 lymphatic glands in the groin, under the arms and behind the ears. That bubonic plague killed 25 million people around the Mediterranean. Later dubbed Black Death, it killed 50 million people 1346-1353, returning to London 40 times in the next 300 years. The third bubonic plague pandemic started 1894 in China, claiming 15 million lives, largely in Asia, before dying down in the 1950s after visiting San Francisco and New York. But it also hit Madagascar in 2014, and the Congo and Peru. The cause, yersinia pestis was identified in...