The Worst Epidemics and Pandemics in History

Also known as the Plague of Galen, this pandemic arose after Roman troops laid siege to a Mesopotamian city. They subsequently spread the disease — whose symptoms consisted of skin eruptions, pharyngitis, diarrhea, and fever — amongst themselves and throughout the Roman empire, leading to millions of deaths.

The Justinian Plague is the first major pandemic caused by the same bacterium, Yersinia pestis, that would cause the Black Death centuries later. Egypt, the Mediterranean, Europe, and the Arabian Peninsula all saw great casualties. Constantinople, which was ravaged by the plague, recorded up to 5,000 deaths a day during the height of the outbreak.

This smallpox epidemic killed a third of Japan’s populace and led to subsequent famine as farmers died or abandoned their fields. After widespread migrations, dislocation, and the deaths of many powerful officials, the Japanese economy took years to recover.

Most likely spread by fleas as well as airborne aerosols, the world’s second known bubonic plague affected much of Eurasia as well as North Africa. The Black Death is known as the most fatal pandemic in recorded history, killing an estimated 75-200 million people on three continents, including up to 60% of the European population.

During the Spanish conquest of the Americas, Conquistadors Hernán Cortés and Pánfilo de Narváez brought the novel smallpox virus — along with their soldiers and slaves — to the New World. The disease wiped out 25-50% of the population of central Mexico, and helped Spain conquer the Aztec empire.