A research team from Northern Arizona University has isolated the probable cause of the plague that terrorized tens of millions 1,500 years ago.

NPR reported on Wednesday that, using DNA extracted from dental pulp, they were able to reassemble the genetic code of the bacteria behind the Justinian plague, named after the Byzantine emperor who saw it overwhelm his subjects -- and nearly himself -- around 541 A.D.

"Some of the estimates are that up to 50 million people died," evolutionary biologist David Wagner told NPR.

Though the pandemic predated the Black Plague by 800 years, the team wrote in the journal The Lancet Infectious Diseases that the two plagues not only emerged from China, but both spread from rodents to humans.

"We conclude that the Y pestis lineages that caused the Plague of Justinian and the Black Death 800 years later were independent emergences from rodents into human beings," they wrote. "These results show that rodent species worldwide represent important reservoirs for the repeated emergence of diverse lineages of Y pestis into human populations."

The team's research was boosted in March 2013, after the discovery of a mass burial site in Munich, Germany, that dated back to Justinian's reign.

"In this particular case, we examined material from two different victims," Wagner told NPR. "One of those victims was buried together with another adult and a child, so it's presumed that they all may have died of the plague at the same time."

[Image: A coin of Emperor Justinian, via Wikipedia Commons]