A long read about how mid-sixth-century Constantinople tried to start producing silk at home — and why that attempt gave rise to one of the handiest legends about stealing someone else’s secret.
Procopius of Caesarea — lawyer, Belisarius’s secretary, author of the History of the Wars and the venomous Secret History — left a short passage in The Gothic War from which the entire story grew. Around 552, under Justinian I, two monks who had spent a long time among “the Indians” came before the emperor. They promised that silk could be produced right in Roman lands, and that they themselves knew how it was done. The point, they explained, was not the trees at all: silk was woven from threads produced by worms. Procopius, a practical man with little taste for miracles, goes on in an almost documentary tone: the eggs of these worms could be preserved and hatched if the newborns were fed mulberry leaves and kept warm.
There is no bamboo in this account, no hollow staffs, no country that can be placed precisely on a map. There is a region the monks call Serinda — a word nobody had used before Procopius, and one he does nothing to explain. There is a promise and a result: the emperor believed them, the monks returned (apparently with eggs), and the empire supposedly acquired silk cultivation of its own. Procopius does not even say how much time passed between the promise and their return — a year, three, five. He almost certainly wrote while the trail was still fresh, at most a decade after the event, and yet he leaves nothing but gaps.
There is one detail here I like: a historian fond of recounting court intrigues does not, this time, name the monks, their place of origin, or the sum they were paid. Either he did not know, or he considered it unimportant. Several centuries later, copyists would find something else unimportant altogether — and it would be these very blanks that they filled in.
To understand why Justinian listened to a pair of wandering monks at all, we need to stop thinking of silk as a rarity in Byzantium. What was rare was the raw material. Byzantines had been weaving silk long before the sixth century: workshops in Constantinople, Antioch, Beirut, and Tyre worked with imported thread. The elite wore silk, the imperial court used it for diplomatic gifts, and heavy purple silk was practically a state monopoly — its color, its pattern, and the right to wear it were strictly apportioned by rank.
The raw material came from far away. During the fourth through sixth centuries, cocoons and threads moved from inner Asia through the oases of Khotan and Sogdiana to the Persian frontier, where Sasanian merchants intercepted them and resold them farther west — with a markup, naturally. Sasanian Persia controlled the chokepoints of the caravan routes and understood its advantage perfectly: silk was something whose price could be raised, whose supply could be held back, or, in lean years, cut off altogether. Byzantium paid both in money and in its loss of independent choice: no Byzantine official could say what the next season would cost.
This gave rise to matters that were fully strategic. Around 531, Justinian sent the envoy Julian to the king of Aksum and the Himyarite rulers of southern Arabia with an idea: intercept the silk before the Persians did — buy it from Indian and Ceylonese merchants and carry it to Rome by sea, through the Red Sea, bypassing Sasanian customs posts. The plan failed: Persian merchants intercepted silk right in Indian ports, buying entire cargoes outright, while the Himyarites found the desert route to the Persian border impossibly burdensome. Later, near the end of his reign, the peace treaty of 562 between Justinian and Khosrow I had to spell out separately the border customs posts and markets through which each side would permit trade — that was how fraught this junction was.
That was the setting in which the two monks made their offer. They had not come with exotic botany, but with the solution to an accounting problem on the scale of a state: how to stop overpaying the middleman. And Justinian, with wars in the West on his hands, permanent tension along the eastern frontier, and the reputation of a court that “yielded to the ancients in nothing” — a man like that was ready to gamble on the risky transport of live cargo.
By the second half of the sixth century, the story had acquired a second version — and it contained the very detail everyone repeats today. The historian Theophanes of Byzantium says that the eggs were brought to Constantinople by a Persian who had come out of the land of the Seres, and that he carried them in the hollow stalk of a plant — narthex, giant fennel. Theophanes’s work has not survived; we know it from excerpts made by Patriarch Photius in the ninth century. Modern retellings have turned the modest stalk into a handy bamboo staff. It is this detail, rather than the fact of the delivery itself, that went viral: it turns the episode into an adventure novel. A hollow stalk is, essentially, a ready-made walking staff: it looks like part of a pilgrim’s or beggar’s traveling gear, it is long, it is empty inside, and it conveniently retains the warmth that keeps the eggs from dying.
Then come new details, absent from both Procopius and the early authors. There appears the motif of monks secretly smuggling the eggs out of a foreign land; speculation that they were perhaps Nestorians fleeing persecution in Persia, perhaps natives of India, perhaps Persian subjects. Someone later moves the date of the event to 553, 554, or 563; someone credits one of Justinian’s officials. In short, the farther from 552 we get, the denser the tale becomes with details — and the more confident its tone grows.
Caution is needed here: later writers did not necessarily “make it up.” They may have drawn on an oral tradition that preserved some real practices for transporting the cargo. But the difference between Procopius’s brief passage and the later versions is enormous, and it tells us something about the mechanism by which information spreads: with every generation of copyists, the report becomes more detailed and more vivid, not less.
The main difficulty begins as soon as we try to pin the event to a geography. Where was Serinda? Some scholars incline to the view that it is a distorted designation for China — from the Latin Seres, “the silk people,” as Romans called the Chinese. Others see the word as a hybrid, accidentally stitched together from “Seres” and “India” — a vague indication of direction: “somewhere out there, where silk and India are.” Still others suggest that it means Khotan, or some region of Central Asia where sericulture had indeed existed since the fourth century.
The identities of the monks cannot be reconstructed at all. We know neither their names nor their faith, neither the country in which they took monastic vows nor the language in which they spoke to the emperor — Greek, perhaps, or through an interpreter. They may have been Syrians, Persians, Indians by origin. They may have been merchants who called themselves monks because that made it easier to gain an audience with the emperor. They may have been monks in earnest. Procopius did not think it worth clarifying, and none of his contemporaries wrote a single line about it.
The cargo itself is unclear. Procopius speaks of eggs. Later versions speak variously of eggs, larvae, cocoons, live moths, or mulberry seeds. Yet this is no minor point: cocoons and moths die much faster on the road than eggs, while silkworm eggs possess a useful property — in the cold, they enter dormancy and can wait out several weeks or even months, if warmed again afterward. It was precisely this biology that made the transport theoretically possible. But we do not know which stage of the life cycle the monks were dealing with, and any route we draw on a map remains speculation.
The route, accordingly, shifts as well. The overland route from Central Asia through Sogdiana and Persia is geographically obvious, but it crosses hostile, or at the very least unfriendly, territory. The sea route through the Indian Ocean, the Red Sea, and Egypt is shorter in distance, but vulnerable to heat, storms, and customs inspections. It is possible that the cargo traveled by a mixed route: part overland, part by sea, changing hands in ports. None of these options is confirmed by the sources strongly enough to prefer it over the others.
What really changes after the middle of the sixth century is the language of the sources. Documents begin to mention “silk workshops” and to suggest that worms were being bred somewhere in the empire. But between “they began trying” and “they began producing” lies a long distance, and it is worth crossing it carefully.
The mulberry, or mulberry tree, is feed — and demanding feed. A silkworm larva eats practically nothing but its leaves, and they must be fresh; wilted or dried leaves are already of little use. That means any silkworm cultivation requires mulberry plantations close to premises where a steady temperature can be maintained. It also requires fairly high temperatures, humidity, protection from drafts, and the absence of predators — from ants to birds. In other words, starting sericulture does not mean releasing moths into a garden. It means building an entire agro-industrial system with climate control — something that, in that age, could only be provided in wealthy, densely built-up places.
The empire understood this and sought to keep the industry under watch. State workshops — gynaecea — were overseen by officials, often worked for the imperial court, and followed rules governing which colors and patterns were permitted to whom. Purple silk was effectively reserved for the emperor, and any attempt by private craftsmen to work with it was punished as the forgery of a state regalia. In this Byzantine system, silk was three things at once: a luxury good, an instrument of diplomacy, and a fiscal resource. Hence the heightened attention: the threads were watched like coin.
Yet — and here begins the dividing line between legend and sources — modern research doubts that the venture succeeded quickly. According to recent work, including an article in the Journal of Global History, we have no reliable evidence of Byzantine sericulture of its own before the 11th century, while dependence on imported raw material persisted right up to the 10th century. That is, the workshops in Beirut and Tyre were operating, fabrics were being made, but the worms, cocoons, and raw thread still came from outside — often through the very Sogdian intermediaries Byzantium had hoped to bypass.
This does not mean Procopius’s report is false. It means “they brought in worms” and “they established an industry” are different events, with centuries possibly lying between them. The Byzantines most likely did try to breed silkworms from the sixth century onward. It was simply not until the 11th century that this effort grew into what could be called independent, full-cycle production.
The most enduring part of the legend is the claim that the Byzantines “stole the secret of silk from China” and thereby supposedly shattered China’s monopoly. Here, several layers need to be disentangled at once.
China was not the only producer by the 6th century. By then, sericulture existed in Korea, Japan, India, and the oases of Central Asia — Khotan, for instance, where, according to tradition, cocoons too had once been smuggled out by not entirely lawful means. So stealing “the secret” meant, at the very least, taking it from hands that were no longer its sole keepers. The Byzantine episode was neither the first nor the last in a long series of attempts to transplant this craft into new soil.
Chinese production did not disappear after 552. It continued to operate, to weave, to export. The silk trade did not cease — it reconfigured itself, as any living trade does when one of its nodes changes. Sogdian merchants did not go anywhere: they moved silk through their networks and, in all likelihood, played a significant role in the transfer of technology itself — both as carriers and as bearers of knowledge about how to handle cocoons. In other words, Byzantine sericulture, if it did take hold, grew up in an environment already saturated with intermediaries.
The scale of the consequences changed over time as well. In the 6th–7th centuries, the effect was more likely localized: one more point appeared on the map of production, costly and vulnerable. By the 10th–11th centuries, the situation was different: Byzantine silk fabrics — dense, brightly patterned, with distinctive ornaments — became an important export and began circulating around the Mediterranean and Europe as gifts, trophies, and goods. By then, the workshops of Thebes and Constantinople were working with local raw material as well, though by current estimates the empire would not be able to reliably supply itself with its own cocoons until the 11th century. So the “theft of the secret” stretches across several centuries, and it would be strange to call one decade the turning point.
What is known for certain about the fate of those exact two monks and that exact cargo is almost nothing. Procopius does not say whether they lived to see the result, whether they received a reward, whether they returned to their former way of life, or ended up attached to the workshops. Perhaps one of them died on the road, and the eggs reached Constantinople in someone else’s hands. Perhaps they returned not in 552, but later, and the entire dating we use is a convention tied to the moment when they were first written about. The fork in the road remains open, and it is more honest to admit that than to build it out with conjecture.
The ending of this story, then, is not about a miracle or a theft. It is about the way the late antique economy was built: as a network of small interlocking decisions. Live eggs in a warm container; calculating what one cocoon costs in gold; two empires disputing the right to levy a duty at a border market; mulberry leaves planted in the right place ten years before anyone needed to harvest them. Each of these decisions on its own is boring. Together, they produce what we call a trade war — and in it, victory goes not to the one who managed to swipe someone else’s secret, but to the one with the patience to grow mulberry trees.