Archaeologists say 12 skeletons found beneath a building site in London could provide evidence of a Black Death burial ground.
The remains were found by teams working on Crossrail - a £15bn project to improve transport links in the capital, including at Farringdon where the bones were found.
Historical records indicate a hastily-built cemetery opened in the area in 1348 as the plague spread across the country.
Up to 50,000 people are thought to have been buried there in less than three years.
Jay Carver, lead Crossrail archaeologist, said: "This is a highly significant discovery and at the moment we are left with many questions that we hope to answer.
"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 London residents, how old they were and perhaps evidence of who they were.
"However at this early stage, the depth of burials, the pottery found with the skeletons and the way they have been set out, all point towards this being part of the 14th century emergency burial ground."
The skeletons were found during excavations below a road in Charterhouse Square.
They were buried in two rows and laid out in a similar formation to skeletons discovered at a Black Death burial site in Smithfield in the 1980s.
Experts at the Museum of London Archaeology will now use DNA testing and carbon dating to determine both a cause of death and a burial date.
Charterhouse Square had previously been identified as a possible site for the lost burial ground, as it is one of few locations in Farringdon to remain undeveloped for the past 700 years.
John Stow, the 16th century historian, said more than 150,000 victims of the Black Death were buried in London, including 50,000 at a site in Farringdon known as 'No Man's Land'.
About 75 million people and up to 60% of the European population are said to have died in the four-year global pandemic.
Archaeologists working on Crossrail have already uncovered more than 300 skeletons near Liverpool Street station.
It is thought they were buried near the site of the Bedlam Hospital in the 16th, 17th and 18th centuries.