Archaeologists work to uncover skeletons from what is understood to be a mass grave for victims of the Black Death. Photo: AFP
London is a city built on bones. From Primrose Hill to the heart of the Square Mile, one need only dig a few yards below the surface to reveal what lies beneath: tens of thousands of bodies, nestled against the foundations of the modern metropolis soaring above them.
Yet this city of skeletons still has the capacity to surprise.
During the past two weeks, engineers working on the £15 billion ($22 billion) Crossrail project have unearthed 14 bodies in Charterhouse Square in Farringdon, revealing a previously unknown Black Death plague pit.
The skeletons lie unmarked in neat little rows. It was the fate of many of the city's poorest inhabitants when plague ravaged Britain from 1348, killing more than a third of its population.
As the bodies piled up and churchyards overflowed, victims were laid to rest in the emergency pits.
The significant find corresponds with historical documents, including John Stow's 1598 Survey of London, that suggest the surrounding area could contain as many as 50,000 bodies, with 100,000 buried elsewhere in the city. No trace of the burial ground has previously been identified.
Archaeologists at the Museum of London are now applying the latest laboratory techniques to the skeletons, including radio carbon dating to establish the burial dates, and attempting to map the plague bacteria.
It is hoped the research will answer many of the questions about the cause of the plague epidemics that cast the shadow of death over London from the 14th century to the mid-17th century. A disease that, as noted by Daniel Defoe in his history of the Great Plague in 1655, reduced the city to "all in tears".
"It is a fascinating discovery," says Royal Holloway's Professor Justin Champion, a specialist in the history of epidemics.
"Nowadays when the skeletons have been dug up we can do so much more. It could be a huge advancement to know more about the Great Plague. We still don't know enough about how it is passed between human beings.
"In some of the poorest areas outside the city walls, such as Southwark and Clerkenwell, people would just drop dead in the street. With a lot of London churches you can see the churchyard is above street level - that is because of the number of bodies underneath.
"During the epidemics, they would have been overwhelmed. They would go from dealing with a handful of deaths to hundreds a week. My guess is a lot of the graves are still there. If you looked, particularly under some of the older buildings, you would find an awful lot more."
About 1.5 million Britons are thought to have died in the Black Death, while about 25 million perished in Europe and an estimated 75 million across the world. Symptoms included nausea, vomiting, fever and horrendously swollen lymph nodes.
During the later epidemics in London, weekly bills of mortality were published detailing the deaths in each parish. Destitute women were employed as "searchers" to enter plague homes and diagnose victims.
When the numbers were high, people would pile into wooden carts and attempt to flee the city. Often they were turned back.
The disease was found in bacteria in the digestive tract of fleas, which fed on the rats that infested London's overcrowded streets. High temperatures and humidity also helped to create a fertile breeding ground.
But could a plague ever strike again? A new study analysing the Great Plague of Marseille, which caused 100,000 deaths between 1720 and 1723, highlights factors that demonstrate we are still at risk.
Vastly increased international trade provides the perfect vehicle for infection to be transported around the world, our cities teem with more rodents and residents than ever before, while genetic changes are increasing the resistance of certain bacteria.
It is estimated that a handful of British people become infected with plague every year, contracted while abroad. There have been several recent cases in America, including a seven-year-old girl in Colorado last September.
But archaeologists have been at pains to stress the newly unearthed bodies in London pose no threat to public health - the bacteria would have perished centuries ago, within weeks of burial.
"It is a great myth that we will disturb some evil grave in London and this disease will come out and kill us all," says Professor Champion. "That is just not going to happen."
Nonetheless, this weekend Londoners may decide to give the plague pits of Farringdon a wide berth.