The Plague of Justinian was a devastating pandemic that struck the Byzantine Empire during the reign of Emperor Justinian I in the 6th century. It is believed to have been caused by the same bacterium that led to the later Black Death, resulting in the deaths of millions and significantly impacting the empire's population and economy. This outbreak began in 541 AD and recurred in waves for several decades. The plague not only caused immense suffering but also influenced the course of history, as it weakened the Byzantine Empire and altered its military and political strategies in the face of external threats.