A rider comes off the steppe at a dead gallop, leaning into the wind, his head and stomach and chest bound tight with strong bands so the pounding of the horse will not break him. The bells on his girdle carry ahead of him, and at the relay post they have heard him coming. By the time he reins in, a fresh horse is saddled and a second man is standing at its head. The dispatch changes hands. The new rider is gone before the dust has settled, riding for the next station some twenty-five miles to the west, and the first man, who has just finished his leg, gets down.
This was the fastest way to move information across the medieval world, and its stations outlived the empire that raised them. The Mongols called it the yam.
The problem of a quarter of the world
By the middle of the thirteenth century, the empire Genghis Khan had built and his sons had extended was the largest contiguous land empire in history — a single dominion stretching from the Pacific coast of China to the gates of Eastern Europe. It is one thing to conquer that much ground on horseback. It is another to govern it. A khan in the Mongol heartland needed to send orders to commanders months of travel away, collect tribute from cities he would never see, and learn that a province had revolted before the revolt could spread. An empire that cannot pass a message faster than an army can march is already coming apart.
The thing that held the Mongol world together was not the famous composite bow. It was a postal network.
According to The Secret History of the Mongols, the empire’s own chronicle, it was Ögedei — Genghis’s third son and successor — who built it. Looking back on his reign, Ögedei named four things he had done after taking his father’s throne: he had finished off the Jin dynasty in northern China; he had dug wells in the dry country so herds and travelers could cross it; he had posted garrisons in the conquered cities; and he had established the relay stations. A rudimentary courier system had existed under Genghis, stitched partly from the older posts the Mongols inherited as they swallowed northern China. In 1234, the year the Jin finally fell, Ögedei turned it into permanent infrastructure: fixed stations across the whole empire, a permanent staff to run them, remounts for envoys and rations set by decree.
Break the route into legs
The principle was relay. No single horse and no single rider had to make the long journey; the journey was broken into legs, and at the seam of every leg sat a station, called an örtöö in Mongolian. The stations sat a short hard ride from one another — usually twenty to forty miles, and Marco Polo, who saw the system at its height under Kublai Khan, put it at about twenty-five. A dispatch could therefore pass through several of them between dawn and dark. Each was a compound with lodging, hot food, and a standing supply of fresh, rested horses.
A messenger rode his leg flat-out, arrived, handed his dispatch to a waiting rider on a fresh mount, and stopped. The new rider carried it on. The message never rested even though the men did. A clerk at each post recorded the hour a courier came in and the hour the next one left, so that any lag could be traced to the station that caused it. Ordinary traffic covered well over a hundred miles in a day this way. The express riders — the ones bound up in their bands, announced by the bells on their girdles so a fresh horse stood saddled before they arrived — could carry a dispatch two hundred miles or more in a day, and as far again through the night.
Between the mounted posts, on the busiest routes, ran foot-runners. Marco Polo described little stations set every three miles, manned by men who ran the distance to the next at speed, each wearing a great wide belt hung all over with bells, heard jingling a long way off. At every post the incoming runner found his relief already standing there, equipped the same way, who took the load off him and sprinted on. A package could move through this human conveyor faster than a single messenger could have carried it.
The reach was staggering for its century. People and messages could be sent along it from Korea to Persia, or from Mongolia down into Vietnam. Word could pass across a continent in the time it took a letter elsewhere to cross a single kingdom.
Ten thousand post-houses
Marco Polo served in Kublai Khan’s administration and wrote down what he saw, and the numbers he gives are enormous. By the end of the thirteenth century, he reported, more than ten thousand post-houses were in operation, and some three hundred thousand horses stood ready in them. The biggest stations on the main roads kept four hundred horses; lesser ones kept two hundred. “At every twenty-five miles of the journey,” he wrote, the traveler found “a station which they call Yamb.”
The horses were not free. Every town and village near a post was assessed for the animals it had to supply and the staff it had to feed, the cost pressed down onto the farmers along the route. The network ran on the backs of the settled people it crossed.
The tablet that opened every door
What entitled a rider to all this — to demand a fresh horse, a bed, a meal, an escort from a village that had never seen him — was a single object he carried: the paiza, a flat inscribed tablet that hung from his belt or his neck. It was the empire’s passport, and rank was written into its very material. The plainer tablets were base metal, inlaid at most with a little silver or gold; above them came silver, then plain gold, and at the very top a gold tablet with a tiger’s head worked into it. A gold paiza announced that its bearer spoke with the authority of the khan himself.
The inscription made the stakes plain. Across the empire the tablets carried a version of the same formula, opening with the words that prefaced every Mongol decree — By the strength of Eternal Heaven — and ending in a threat. The edict of the khan, they declared; he who shows it no respect shall be guilty. To refuse a paiza-bearer was to defy the khan, and everyone who could not read the script still understood what defying the khan cost.
The Mongols did not invent the idea — the Liao, Jin and Xi Xia dynasties had issued tablets of authority before them. What was new was the scale it now worked at: a single badge that a man could carry from the Pacific to Persia and have honored the whole way, across every language and every conquered people in between.
What it cost the people it crossed
A system that gives men the right to seize horses and lodging from strangers invites abuse, and the yam was abused badly. Officials and nobles issued paizas they had no business issuing. Envoys requisitioned horses and supplies with impunity, taking more than their due. Thieves stole the tablets and decrees off envoys, impersonated them, and plundered the stations outright; some sold the post horses as their own. Governors, pleading the cost of all these visitors, levied taxes on the peasants beyond what the posts required and pocketed the difference. Merchant companies traveling under Mongol sponsorship drew on the stations too, until Möngke sent inspectors to watch them and barred them from the relay and its tablets altogether.
The khans understood the rot and kept trying to cut it back. Ögedei had already moved to stop the nobility from handing out tablets at will. Decades later in Persia, the Ilkhan Ghazan attacked the problem in detail: he recalled the old paizas, issued new ones stamped with the bearer’s own name so they could not be passed around, required officials to surrender them when their posting ended, and ruled that only envoys carrying urgent military intelligence could draw on the staffed relay at all. The decrees tell their own story — the system was indispensable enough to be worth reforming again and again rather than abandoned.
Reinvented, not improved
The yam outlasted the unity of the empire that made it, its stations absorbed and maintained by the successor states that carved up the Mongol world. Its logic — break the route into legs, keep fresh horses standing at every seam, let the message run while the riders rest — was so sound that it would be reinvented, not improved upon, centuries later. When the American Pony Express strung its relay posts across the West in 1860 and astonished the country by carrying mail from St. Joseph to Sacramento in ten days, it was running, without knowing it, the same machine the Mongols had built six hundred years before: stations ten to fifteen miles apart, a fresh horse at each, riders spelling one another so the mail never stopped. Nearly two thousand miles in ten days works out to about two hundred a day.
Which is to say that the fastest mail in nineteenth-century America moved at roughly the speed of a Mongol courier with a tablet at his belt — and lasted eighteen months before the telegraph closed it, while the yam had run for centuries.