History's first recorded pandemic struck the Byzantine Empire in 541 AD

The Plague of Justinian, likely caused by the same bacterium behind the later Black Death, swept through Constantinople and the Mediterranean world starting in 541 AD. The contemporary historian Procopius described thousands dying per day at its peak; modern estimates put the death toll at tens of millions across the empire and beyond.

— Procopius of Caesarea, History of the Wars, Book II — 6th century AD