The teeth from skeletons uncovered during a London railroad makeover have revealed new information about the black death that plagued Europe centuries ago.

While doing work on a new railroad system in London, The Associated Press reports that construction workers came upon a gruesome discovery: 25 buried skeletons. Archaeologists were immediately called to the scene and suspected that the skeletons were part of a mass grave for plague victims, due to the location of the burial site near an undisturbed monastery.

Scientists began by examining the teeth of the skeletons, pulling the DNA from the remains to search for a cause of death. The DNA showed the presence of the plague virus, Yersinia pestis, in most of the remains. Don Walker of the Museum of London said, "It’s fantastic we can look in such detail at an individual who died 600 years ago.It’s incredible, really," as the scientists were able to pull more information from the skeletons. Those who were buried in the grave were poor laborers, shown in the malnutrition of the teeth and in back injuries from a lifetime of work."The combination of a poor diet and generally a struggle means they were very susceptible to the plague at that time and that's possibly one of the explanations for why the Black Death was so devastating," said Jay Carver, another researcher on the case.

BBC News reports that the Black Death hit Europe with a vengeance from 1347 to 1351, killing off nearly half the population. The skeletons in the grave were found to have been buried in different time periods, some during the initial outbreak, and some during a later infestation in the 1430s.