Plague of Justinian: 30-50 million people (541-549)
The disease – now confirmed to be bubonic plague – reached Constantinople, capital of the Late Roman or Byzantine Empire, in 541 AD. It was soon killing 10,000 people a day. Corpses littered public spaces and were stacked like produce indoors. It was perhaps the first major outbreak of bubonic plague the world had seen and the record suggests that it extended across continents, reaching Roman Egypt, the Mediterranean, Northern Europe and the Arabian Peninsula.