The Bubonic Plague of Justinian

In The Guardian and elsewhere: a new journal article in the Lancet identifies the sixth-century Plague of Justinian as Yersinia pestis.

Professor Edward Holmes, from the University of Sydney, was one of the authors of the study, and said it was the oldest pathogen ever sequenced.
"This is the first complete genome from one of the most significant disease events in human history," he said.
The results showed the strains from the plague victims were distinct from those involved in the Black Death, the later pandemic which killed an estimated 60% of the European population.
The Justinianic strains appear to be an evolutionary “dead end” when compared with modern strains, and most likely originated from Asia and then spread to Europe along trade routes such as the Silk Road.