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).[8][9] The latter was much shorter, but still killed an estimated one-third to one-half of Europeans. Ancient and modern Yersinia pestis strains closely related to the ancestor of the Justinian plague strain have been found in Tian Shan, a system of mountain ranges on the borders of Kyrgyzstan, Kazakhstan, and China, suggesting that the Justinian plague may have originated in or near that region.[10][11]