The mass grave was discovered during archaeological work associated with the Crossrail project, a new line being built in London, the Daily Mirror reported. Archaeologists said pottery found with the skeletons dates from about 1350 and the layout of the bodies suggests a mass grave during an epidemic.
About 1.5 million people are believed to have died in Britain in the bubonic plague epidemic that peaked in 1348. The plague killed about one-third of the population of Europe.
By Thursday, 13 skeletons had been unearthed at the site in Charterhouse Square in Smithfield. A similar mass grave was found nearby almost 30 years ago.
Jay Carver, the lead archaeologist, said the find could be critical to research on bubonic plague and its history.
"Scientists hope to map the plague virus DNA. Biologists are researching ancient diseases in the hope of better understanding modern ones," he said.
Archaeologists hope that as they dig deeper they will also find remains of Roman London in the square.