After construction workers digging tunnels for the new Crossrail train line in 2013 discovered some 25 skeletons buried under Charterhouse Square in the Clerkenwell area of London, scientists immediately suspected they had stumbled on a plague cemetery.
The square, once home to a monastery, is one of the few London areas that have remained undisturbed for hundreds of years, and the location outside the walls of medieval London coincided with historical accounts. To test this theory, scientists extracted DNA from one of the largest teeth in each of 12 skeletons. Testing showed evidence of Yersinia pestis, the bacterium that causes the plague, which confirmed that the individuals buried underneath the square had likely been exposed to—and died from—the Black Death.
The plague still infects several thousand people every year around the world, though most patients recover if treated early enough with antibiotics. When they compared the strain of plague preserved in this medieval DNA with the strain that killed some 60 people in Madagascar in 2014, however, they found something surprising. The medieval strain was no stronger than the recent one; in fact, their genetic codes matched almost exactly.
