How the Mongols Ran a 5,000-Mile Postal Network

By 1279, Kublai Khan's government was running roughly 1,400 relay stations — called yams — spaced about 25 to 30 miles apart from the Black Sea to the Pacific. Each station stocked a few dozen horses, a small crew, and a bed for the night. A rider carrying a paiza, a brass or silver tablet marking his authority, could swap exhausted mounts at every station and ride again.

The routine pace was about 100 to 125 miles a day. Urgent dispatches — tied with a cord to a small bell the rider rang to demand right of way — could cover 200. Marco Polo described the system in detail after seventeen years in the khan's service, and counted stations personally along the routes he traveled. His numbers are close to those preserved in the Yuan Shi, the official Mongol-Chinese dynastic history compiled in 1370.

Ogedei Khan had formalized the network in the 1230s, but it worked because of what Genghis built first: a treaty system, the Yassa law code, and the blunt principle that anyone who killed a Mongol envoy got the nearest city razed. Ambassadors traveled faster because no one dared rob them.

The Yam carried tax receipts, military orders, plague reports — and eventually the plague itself. The Black Death reached a Crimean trading post in 1347 along a route fed and protected by the postal infrastructure. Within five years it had killed roughly a third of Europe.

The Qing dynasty kept the Chinese section operational into the 19th century. Russia adapted the institution wholesale; in modern Russian, a postal station is still called a yam.