[Chronicles] Serious epidemics can have far-reaching social, cultural, and geopolitical consequences. The plague which devastated Athens in 430 BC‐in the second year of the Peloponnesian War, when an Athenian victory still seemed within reach‐claimed a quarter of the population, some 75,000 people including Pericles. His successors were weak and incompetent, and Athens suffered a precipitous decline in the observance of "every rule of religion or law," according to Thucydides. Not until 415 B.C. had Athens recovered sufficiently to mount a major offensive, but due to the poor quality of Pericles’ successors the Sicilian expedition ended in an utter rout.The Antonine plague (A.D. 165-180) was actually caused by smallpox rather than Yersinia pestis. It took up to five million lives, about 25 percent of those affected. Approximately one-tenth of the population of the Empire died, more than a third in some regions (Gaul, Lombardy, the Rhine Valley). The Roman army was devastated, leaving frontiers vulnerable to barbarian penetrations. Germany’s leading early historian of ancient Rome Barthold Georg Niebuhr concluded in 1827 that "the ancient world never recovered from the blow inflicted on it by the plague which visited it in the reign of Marcus Aurelius." It was the precursor of the Third Century Crisis and the subsequent long-term decline of Rome’s power and authority.
The Black Death (1347-1351) killed 30 to 60 percent of Europeans and caused massive religious, social, and economic disruptions. In the 17th century it struck again, with deadly ferocity but not the same geographic reach. Its effect on the city of Milan was presented with impressive accuracy in Alessandro Manzoni’s 1828 I Promessi sposi (The Betrothed), Italy’s equivalent of Tolstoy’s War and Peace.