Crossrail workers are shocked to discover 13 skeletons buried under a square in the City of London - and archaeologists say a mass grave containing the bones of 50,000 people could be nearby.

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Video: Archaeologists Dan Walker from the Museum of London Archaeology, and Jay Carver from Crossrail, discuss the find.

The 13 bodies met their unfortunate demise almost seven centuries ago, when the plague swept through Europe and killed over a quarter of the British population in 1348.

But it was a piece of pottery found in the graves which dates back to around 1350, as well as the neat layout of the bodies in two rows, that gave archaeologists the clues as to when - and why - they died.

The skeletons were found lying in neat rows under Charterhouse Square in Farringdon, 2.4 metres below the road, during excavation work for London's £14.8bn Crossrail project. And according to archaeologists, there could up to 50,000 more skeletons buried nearby.

"The short answer is we don't know just how many skeletons are out there," said Nick Elsden from Museum of London Archaeology (MOLA) adding that more discoveries are likely.

Tests will be carried out on the bones after their excavation but experts are linking the discovery with the Black Death as records show that a burial ground for plague victims was opened in the Farringdon area. Scientists are also hoping the skeletons will contain traces of DNA that may help to find out more about the virus which caused the Black Death.

'Emergency burial ground'

Crossrail lead archaeologist Jay Carver said this was a "highly significant discovery".

"We will be undertaking scientific tests on the skeletons over the coming months to establish their cause of death, whether they were plague victims from the 14th century or later residents, how old they were and perhaps evidence of who they were.

The short answer is we don't know just how many skeletons are out there. Nick Elsden, Museum of London Archaeology

"However, at this early stage... all points towards this being part of the 14th century emergency burial ground."

In nearby east Smithfield, a similar skeleton formation was found in a Black Death burial site in the 1980s.

And these are not the first skeletons to be discovered as part of the Crossrail project, which aims to build a high-speed rail network across London, with 37 stations, by 2018. Archaeologists uncovered 300 skeletons at a known burial ground at Liverpool Street, which dates from the 1500s to 1700s, near the Bedlam Hospital.

And for anyone worried about coming into contact with the Black Death skeleton pit, Mr Elsden was quick to reassure the public that there was no longer any health risk from the plague.

"It's not something that stays in the soil," he said. "You have to actually meet someone who has it in order to catch it."

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