"Scientists have reconstructed the genetic code of a strain of bacteria that caused one of the most deadly pandemics in history nearly 1,500 years ago. They did it by finding the skeletons of people killed by the plague and extracting DNA from traces of blood inside their teeth. The plague swept through Europe, northern Africa and parts of Asia. Historians say that when it arrived in Constantinople, thousands of bodies piled up in mass graves. People started wearing name tags so they could be identified if they suddenly collapsed."