Eight hundred years before the notorious Black Death plague, another pandemic devastated Europe. The Justinian plague wiped out up to half the population and is thought to have contributed to the fall of the Roman Empire. But not that much had been known about it — until now. Dr. Hendrik Poinar, an evolutionary geneticist at McMaster University, analysed the teeth of people thought to have died of the Justinian Plague. He managed to uncover its cause: Yersinia pestis, the same bacteria responsible for the Black Death. But it is a completely different strain than the one that caused the Black Death, and it is now extinct.