Scientists studying the remains of 25 skeletons from medieval London say they’ve helped fill in some of the gaps surrounding Europe’s Black Death plague, one of the worst pandemics in human history. DNA evidence extracted from the 660-year-old skeletons suggests that the disease, commonly thought to have been spread by fleas living on rats, was actually an airborne infection spread from person to person by coughing and sneezing, the Guardian reports.

The skeletons were unearthed last year during construction of London’s new Crossrail, a 118-kilometer, or 73-mile, railway connecting east and west London. Archaeologists discovered 13 skeletons wrapped in shrouds and arranged in neat rows underneath Charterhouse Square in Farringdon. Later, 12 more skeletons were uncovered, bringing the total to 25.

Researchers immediately speculated that the remains probably belonged to victims of the Black Death, which swept through Europe during the mid-14th century and killed an estimated one-third of England’s population. Records indicated that as many as 50,000 victims of the plague were buried in the cemetery in London’s Farringdon district. The bodies found in Farringdon were believed to have been buried between 1348 and 1349.

Now, DNA analysis of the skeletons has shown that the bones were indeed victims of the Black Death. Researchers found that the skeletons’ teeth contained genetic material from the plague bacterium Yersinia pestis. The research has helped scientists piece together what happened during the infamous plague’s darkest days.

“Analysis of the Crossrail find has revealed an extraordinary amount of information, allowing us to solve a 660-year mystery,” Jay Carver, Crossrail’s lead archaeologist, told Reuters. “This discovery is a hugely important step forward in documenting and understanding Europe’s most devastating pandemic.”

Among researchers’ findings were that many of the skeletons showed signs of malnutrition and spinal damage, suggesting that the people were manual laborers. Some of the skeletons showed high rates of upper-body injury, indicating involvement in violent confrontations.

Thirteen of the skeletons were male, three were female and two were children. The genders of the other skeletons couldn’t be determined.

Scientists say the skeletons provide historians with a rare window into the daily lives of medieval Londoners.

"We can start to answer questions like: where did they come from and what were their lives like?” osteologist Don Walker, of the Museum of London Archaeology, told the BBC. "I'm amazed how much you can learn about a person who died more than 600 years ago."

Perhaps most intriguing was the finding that the strain of plague bacterium found in the skeletons’ teeth was nearly identical to one that recently killed 60 people in Madagascar. The Black Death killed between 75 million and 200 million people in medieval Europe in just a few years’ time. For a plague to have spread so quickly, researchers argue, it would have had to have been airborne. This suggests the Black Death was a pneumonic rather than bubonic plague, with infections having spread from one human to another rather than from fleas to humans.

"As an explanation [rat fleas] for the Black Death in its own right, it simply isn't good enough. It cannot spread fast enough from one household to the next to cause the huge number of cases that we saw during the Black Death epidemics," Tim Brooks, a scientist from Porton Down, told the Guardian. Brooks’s theory will appear in an upcoming Channel 4 documentary, "Secret History: The Return of the Black Death."

"What's really exciting is the bringing together of many different lines of evidence to create a picture of such a devastating world event as the Black Death," Carver told Reuters. "Historians, archaeologists, microbiologists, and physicists are all working together to chart the origins and development of one of the world's worst endemic diseases and help today's researchers in ancient and modern diseases better understand the evolution of these bacteria."