A mass burial pit of victims of the Black Death dating back to the 14th century has been discovered near Immingham in Lincolnshire.

Archaeologists from the University of Sheffield were searching the site of Thornton Abbey, once one of the country’s biggest medieval abbeys, for evidence of a post-medieval building when they came across the grave containing 48 skeletons, 27 of them children.

Carbon dating shows the remains are from the middle of the 14th century, when the Black Death, which was most probably bubonic plague, killed an estimated 75 million to 200 million people across Europe and Asia.

Teeth samples were sent to Canada where DNA was successfully extracted and tested positive for Yersinia pestis, the bacterium responsible for the plague, which is documented to have reached Lincolnshire in the spring of 1349.

Despite the devastating impact of the plague – up to half the population of England may have perished during the Black Death – Yersinia pestis has only previously been identified at two 14th-century sites, both cemeteries in London where the civic authorities were forced to open new emergency burial grounds to cope with the very large numbers of urban dead.

Facebook Twitter Pinterest Illustration of a mass burial, where more than half of the skeletons are children. Photograph: University of Sheffield/PA

Dr Hugh Willmott, from the University of Sheffield’s department of archaeology, has been working on the Lincolnshire site since 2011 and directed the excavations. He said: “The finding of a previously unknown and completely unexpected mass burial dating to this period in a quiet corner of rural Lincolnshire is thus far unique, and sheds light into the real difficulties faced by a small community ill-prepared to face such a devastating threat.”

Explaining why more such sites have not been found before, Willmott said one reason was that despite the number of plague deaths, communities were determined to give people a proper burial, normally in the parish churchyard.

“Mass burials are a signal of when the system has broken down,” he said. “This community had obviously reached a point where it could not cope.”

Facebook Twitter Pinterest It is hoped that further analysis will determine whether any of the people in the pit were related. Photograph: University of Sheffield/PA

Despite a common perception that mass burials involve throwing bodies on top of each other, the skeletons at the Lincolnshire site were carefully laid out in rows to make efficient use of space.

As they included men, women and children it was clear they were not from the abbey but possibly from a monastery hospital believed to have also been on the site.

Because the plague killed people within three to five days, it is likely that family members brought their relatives to the hospital in the hope that they would be administered the last rites and get a decent burial.

It is hoped that further analysis will determine whether any of the people in the pit were related, what they did for a living and their diet, the latter through isotope analysis.

Willmott said the placement of some of the children overlapping adults indicates that there may have been family members.

“We don’t focus just on their deaths. Archaeologists tend to see the point as learning about these people in life. We know now they died from the Black Death but this was a living, breathing community. What can these skeletons tell us about their lives before their funeral?” he said.