The Plague of Justinian was a devastating pandemic that struck the Byzantine Empire in the 6th century, beginning in 541 AD. It is believed to have been caused by the same bacterium, Yersinia pestis, responsible for the later Black Death. The plague spread rapidly through trade routes, leading to high mortality rates and significant social and economic disruption. Named after the Byzantine Emperor Justinian I, the plague recurred in waves for nearly two centuries. Historical records suggest that it killed millions, with some estimates indicating that up to 25 million people may have perished. The epidemic had lasting effects on the population and the empire's stability.