What caused the fall of the Roman Empire? A devastating plague that struck during the reign of Emperor Justinian in 541 AD, killing a quarter of the population, seems to have landed the final blow, but the identity of the infection was a mystery.

Now sequencing of DNA taken from two skeletons buried in Bavaria, Germany, in the 6th century has uncovered the complete genome of Yersinia pestis, the bacteria also blamed for the Black Death that struck Europe in 1348. The find suggests that Y. pestis may have emerged to ravage humanity several times.

Hendrik Poinar at McMaster University in Hamilton, Canada, who led the team that sequenced the German bacteria, also helped sequence Y. pestis bacteria from Londoners killed by the Black Death. He says the new finds don't prove Y. pestis was the sole cause of both plagues, but "make it more likely Yersinia was part of the larger story"....