The First Plague Pandemic was the first Old World pandemic of plague, the contagious disease caused by the bacterium Yersinia pestis. Also called the Early Medieval Pandemic, it began with the Plague of Justinian in 541 and continued until 750 or 767; at least fifteen or eighteen major waves of plague following the Justinianic plague have been identified from historical records. The pandemic affected the Mediterranean Basin most severely and most frequently, but also infected the Near East and Northern Europe. The Roman emperor Justinian I's name is sometimes applied to the whole series of plague epidemics in late Antiquity, as well as to the Plague of Justinian which struck the Eastern Roman Empire in the early 540s.