How Silk Helped the Armies of Genghis Khan Conquer Asia

At least until the spring of 1221, Merv, now in Turkmenistan, from which the tiny eggs of Bombyx mori had moved to Persia and the lands to its west, was still a most splendid city. Around March 6 of that year, it ceased to be so.

Genghis Khan had taken its golden throne and ordered the city burned to the ground. Its sweet watermelons were no longer cut into strips and dried on its washing lines; scholars put down their pens and abandoned its libraries; astronomers scattered from the observatory; poets forgot their words; and weavers left their looms still interlaced with unfinished fabrics of silk and cotton and ran from their workshops along the still waters of the Majan Canal. All Mongol soldiers were issued a decree from the khan such that each was to end the lives of three to four hundred distraught souls.

“That city,” it was said, “which had been embellished by great men of the world, became the haunt of hyenas and beasts of prey.” Smoke rose over its palaces and groves, gardens and streams. Books that had held the learnings of centuries blackened and curled in the intense heat, before crumbling into ash. Its canals were destroyed, orchards of its celebrated fruit trees felled, oasis fields that produced its sweetest watermelons salted.

Genghis Khan ordered a call to prayer from a minaret to root out anyone who had found a clever place to hide and had them slaughtered; and then he ordered a count of the dead that came in at 700,000 bodies of all ages—or, perhaps, parts thereof. “It was the last day of the lives of most of the inhabitants of Merv,” pronounced a Persian historian who had allied with the Mongols. By the end, only a small number of its sophisticated citizens would survive. Those who did had been intentionally kept alive. And all of them, it is said, were artisans.

Over its long history, many had seen and coveted the bountiful treasures of Merv. Occasionally, its walls had failed to deter these others who, before the Mongols, had also sought its wealth or its political prestige. Some seventy years before Genghis Khan and his son plundered and murdered their way through Merv, it had been the turn of the Oghuz, or Ghuzz Turks, a people whose descendants would found the Ottoman Empire.

For three days they helped themselves to the contents of Merv’s treasury and stores. Nothing of any value was overlooked, but it was on the first day that their chests were filled with what they considered most precious. Along with the city’s gold, the very first things to be pillaged were its famed silks, loomed of threads pulled from boiling cocoons between the long fingers of its artisans.

When Genghis Khan died in 1227, perhaps even greater than the vast empire he had forged was the complete dominion of the network of roads that came with military conquest. Across these silk roads—as, many years later, they would come to be known—traders’ caravans traveled no less efficiently than the Mongol blade, moving porcelain and jewels, gunpowder and horses, people to be enslaved, Marco Polo and the bubonic plague. There was also paper, an incredibly valuable commodity that had been invented in China some thousand years before Genghis Khan was born. And, of course, traded along these roads for magnificent profit were bales of perfectly crafted silks from China, as well as from wherever Bombyx mori feasted on mulberry leaves across Central Asia.

But for Genghis Khan, such people as he had studiously kept alive in Merv—its artisans—may also have had a significance beyond the spoils of war and the trappings of wealth, one upon which the very survival of his warriors might depend. Theirs were swords that would not rust and horses that could not rest, and their soldiers—all males older than fourteen who were neither doctors nor priests—were provided with armor designed to keep them light enough to stay agile and yet strong enough to return safely to the horde, to prevent casualties among their own. Breastplates and backplates of leather were sewn together like scales, with a leather-covered shield and helmet usually made of much the same. The outfit weighed nowhere near the fifty kilograms or so of the iron mail worn by European cavalry at that time, putting additional weight on their already burdened horses.

Much of a battle against Genghis Khan’s hordes would take place after a soldier dismounted—or was dismounted by the iron tip of a Mongol javelin, the terrifying momentum of a swinging axe, or any of the sixty arrows with which Genghis’s men were also armed. If this Mongol armor that speeded them onto golden thrones had no need of chains wrought from iron wires it was because of what was under their leather-scaled cuirass. It was something better than other types of underarmor that were made of linen quilted with wool or horses’ hair because it was smarter.

The idea for the Mongols’ choice of fabric had been appropriated from Chinese warcraft. It was to take the extraordinarily light thread extruded from the insect that Neolithic China’s farmers had domesticated so long before, and with it craft an undershirt, standard issue, of tightly woven Bombyx mori silk. Compared to the promise of cold, hard metal armor, and although it may have been layered, the sheerness of silk cloth seemed to offer little deterrent against the sharp ends of enemy weapons, even if it did allow them more rapid onslaughts and escapes. But it was extraordinarily effective.

Were the leather body armor to be penetrated, the fine silk undergarment would wind tightly around the heads or points of sharp missiles that might otherwise have pushed deeper into limbs or through them. More often than not, an arrow would not actually break through this fabric so surprisingly delicate to the touch. Removing an arrow, particularly one that was barbed, inevitably caused a larger wound than the offending object itself had, and, with it, extensive bleeding out.

But when an arrow had embedded itself first in silk, the tightly woven threads around the wound would be pulled instead, turning the arrowhead, gently teasing the weapon out and minimizing further damage. As the Mongols herded the newly enslaved or slaughtered those who were unfortunate enough to be in their way, the lives of their own soldiers were much less likely to be lost thanks to their undershirts.

But the doctors serving the armies of the khan may also have noted that wounds into which fine Bombyx mori silk was dragged by the sharp end of an arrow might also have been better equipped to mend themselves. Simply breaking the skin is to create a crack in the wall of the body’s strategic defense, an opening of which the forces of infection take full advantage. Where there is a wound—warm and moist, divested of the first line of defense of intact skin—there is also an ideal opportunity for bacteria to invade and colonize. This attack the immune system must find a mechanism to avert.

Under the broken surface, the journey of a physical trauma that heals is an intricate, programmed process built of an exact sequence of steps that the body completes through the conversations of myriad cells. Here are hormones, signals, and the fine architecture of tissues that must work in concert in a precise order. There is constriction of blood vessels, a spike in heart rate and in the cells that work to inflame and so repair, cells that move and recruit others to help, that rebuild broken blood vessels and new tissue in the place of the old; the matrix that formed the cavity of the wound slowly remodels into a new structure that seals, regenerates, and binds broken muscle and nerves, bone and skin.

In one sense, the cocoons of Bombyx mori are not so different from skin. The cocoon exists to protect, not just because it forms an impenetrable layer that covers important structures within, but because in the deep structure of silk appear to be embedded proteins that are antiviral, and yet others that can damage the fortressing walls of bacterial cells. These are defenses that protect the silkworm pupa as it metamorphoses into its adult form, but they are also retained in the silk unreeled from its cocoon, spun by human hand into yarn; the fabric of silk woven from those threads made in exactly the same way that the Chinese had developed it so long before: first stripping from it, by special boiling, the part called sericin, the cement that binds the strands of silk protein as it emerges from its silkworm, so that silk can interact with every stage of the complex healing process. Both the fibroin that forms the silk and the sericin that binds it can hasten the healing of wounds.

But with sericin intact, an inappropriate, heightened immune response might be sparked in the injured, one that could induce an allergic reaction. The Chinese, already having removed this cement, as far as can be told, had been spinning silk threads to suture wounds for around two thousand years by the time the Mongol campaigns began; the silk also served as dressings whose threads could stimulate the cells that repair and rebuild to convene and proliferate in the wound bed.

In a future time, some eight hundred years after the death of the khan, silk without sericin, and even the sericin routinely discarded in the manufacture of silk, would be manipulated by doctors and engineers. They would create sponges and gels; films and mats of silk as scaffolds seeking to support wounds that struggle to heal; matrices for the regrowth of blood vessels and broken skin; formulations to attract cells as they migrate and regenerate. And all of this from the sophisticated manipulation of the extracts of a little silkworm.

But before all that, the simple silk underclothes of the Mongols had only been intended to prevent the death of one more fighter, to stem the catastrophic loss of blood from an agile horseman riding into the path of an enemy arrow. That it was even possible for the fine threads of an insect’s cocoon to halt the flow of blood, and even the flight of a missile designed to kill, would be backed up by observations made, quite by chance, and published exactly 660 years after the death of Genghis Khan, over six thousand miles away, in Arizona Territory in the American Old West.

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From Silk: A World History by Aarathi Prasad. Copyright © 2024 by Aarathi Prasad. Reprinted by permission of William Morrow, an imprint of HarperCollins Publishers.