The Black Death Rides the Trade Routes

The trade networks of Units 2.1 through 2.5 moved more than silk, spices, and silver. The Mongols had linked East Asia to the Mediterranean with safe, fast overland routes, and sea lanes connected the Indian Ocean to the Black Sea. Those same roads and ships could move a pathogen just as efficiently as a bolt of cloth. Yersinia pestis, the bacterium behind the plague, had circulated among rodent populations in Central Asia for ages. Mongol expansion and the resulting boom in long-distance contact gave it a highway into dense, unprotected cities.

The outbreak that reached Europe is usually traced to the Mongol siege of Caffa, a Genoese trading post on the Black Sea, in 1346. From Caffa, Genoese ships carried the plague to Sicily by October 1347. It reached Marseille and Tunis by early 1348, spread through Paris and London by late 1348, and kept pushing outward, reaching Norway by 1349 and Moscow by 1351. The pattern followed shipping lanes and overland trade roads almost exactly, port cities first, interior regions later.

The human chain ran: flea bites an infected rodent, flea carries the bacterium, rat carries the flea onto a ship or caravan, ship or caravan carries the rat into a city, flea jumps to a human and bites. Rats alone could not cross oceans or deserts; they needed the infrastructure traders had already built. The result reshaped Europe. Population fell from about 80 million before 1347 to roughly 50 million by 1353, a drop near 40 percent. Labor became scarce, survivors could demand wages or better terms, and that pressure helped crack open the system of serfdom across Western Europe in the following century.