Yersinia pestis
In 2013, researchers confirmed earlier speculation that the cause of the Plague of Justinian was "Yersinia pestis", the same bacterium responsible for the Black Death (1347–1351). Ancient and modern "Yersinia pestis" strains closely related to the ancestor of the Justinian plague strain have been found in the Tian Shan, a system of mountain ranges on the borders of Kyrgyzstan, Kazakhstan, and China, suggesting that the Justinian plague originated in or near that region.