Archaeologists started excavating around 3,000 skeletons and Roman artifacts at a Crossrail construction site at London's Liverpool Street station. (Reuters)

The bones have been resting beneath layers of London soil for centuries, largely undisturbed since buried there during plague outbreaks. Soon, they will all be dug up so a train line can run through the site.

Archaeologists began the excavation Monday and expect to recover the skeletons of 3,000 people, many of whom are believed to have perished during bubonic plague outbreaks, including the "Great Plague" that devastated London in 1665.

“It’s going to be archaeologically the most important sample we have of the population of London from the 16th and 17th centuries,” Chief archaeologist Jay Carver told the Associated Press.

Bedlam, which was used from 1569 to at least 1738, was London's first municipal cemetery and became an overflow burial site during four plague outbreaks. But it was also a burial ground for those without other options, including those who couldn't afford a church burial or were refused burial elsewhere for religious or political reasons, according to the Museum of London Archaeology, which is overseeing the field dig. Members of Levellers political movement were also thought to have been buried there.

[After 8 centuries, rats exonerated in spread of Black Death. Gerbils implicated.]

A handful of patients from nearby Bethlehem Royal Hospital, often called Bedlam Hospital, were also buried at the site. Bedlam Hospital, which opened in 1247 but has since relocated, was one of the world's oldest asylums for the mentally ill.

Many of those buried at Bedlam are thought to be victims of the plague. The Black Death of 1348 predates the burial ground's use, but there were numerous plague outbreaks in the years that followed. The last major outbreak, the Great Plague, began in February of 1665 and wiped out a fifth of London's population, killing 100,000 within seven months. From the Museum of London:

Many fled the capital to escape the disease. Victims were shut in their homes and a red cross was painted on the door with the words ‘Lord have mercy upon us’. The theatres and other public entertainments such as football were banned to stop the disease spreading...

Between one and three people died in most infected homes. In extreme cases whole families died. People were terrified of the disease; some threw sick servants into the streets, others refused to help sick friends and family. Samuel Pepys wrote in his diary, ‘the plague [is] making us cruel as dogs to one another.’

Skeletons of a mother and child found in the Bedlam burial ground on the future site of a Crossrail ticket hall. (Reuters/Suzanne Plunkett)

Researchers hope that the remains will be a trove for scientific discovery on what life was like for Londoners, including their diet and migration patterns.

Bones recovered during previous digs have given clues as to why the Black Death spread and claimed so many lives; scientists examining the remains of 14th century victims of the Black Death said last year that the disease appeared to have been airborne, rather than spread by flea bites. A number of those skeletons were also traced to people from far-off places, and nearly all had back damage, suggesting heavy manual labor.

A team of 60 people working daily in two shifts have been dedicated to the Bedlam job, Carver said in a video about the project. The dig will last four weeks, and the entire field project, which will also recover artifacts from an ancient Roman road that rests below Bedlam, is expected to finish in September.

"Unwrapping these individual skeletons, which are lying on top of each other, sandwiched together, is an extremely tricky process," Carver said in the video.

[Everything you know about the Black Death is wrong]

Once the skeletons are tested by museum workers, they will be reburied at a site on Canvey Island, AP reported.

"When you are doing something like this, you do feel a connection with them,” Alison Telfer, a Museum of London Archaeology project officer, told the AP. “I think you have a responsibility to treat them with great respect. It’s quite a special process.”

The massive Crossrail project will span more than 100 kilometers and run through 40 train stations. But it's also become the country's largest archaeology project and has been a treasure hunt for scientists who have recovered more than 10,000 artifacts at 40 sites, according to the Museum of London Archaeology.

"Construction for Crossrail is providing rare and exciting opportunities for archaeologists to excavate and study areas of London that would ordinarily be inaccessible, such as under established road-systems," Nick Elsden, a Museum of London Archaeology project director, said in a statement. "There are up to six metres of archaeology on site, in what is one of the oldest areas of the city, so we stand to learn a great deal.”

And by 2018, commuters can hop on a modern train where a plague burial ground once stood.


Archaeologists work in the Bedlam burial ground on the future site of a Crossrail ticket hall next to Liverpool Street Station in London March 6, 2015. (Reuters/Suzanne Plunkett)

An artist's impression of the new Liverpool Street Crossrail station. The Bedlam excavation will allow construction of the eastern entrance of the new Liverpool Street Crossrail station. (EPA/Crossrail/Handout)

MORE READING:

200 skeletons found in medieval mass grave beneath Paris supermarket

Historian believes bodies of 800 babies, long-dead, are in a tank at Irish home for unwed mothers

DNA evidence proves that King Richard III’s remains really did end up in a parking lot