two-body problems, as they are known, are simple, elegant, and most of all, unique.

Add even one more body to the system, however, and the solution is no longer unique.

The obvious inference is that a common sovereign is a far more effective force for union than a common enemy, and the absence of that sovereign—the absence of Imperial Rome—permitted the pieces of Europe to define themselves based on local, rather than universal, characteristics. (Pg.5)


Pelusium 540 During these times, there was a pestilence, by which the whole human race came near to being annihilated. Now in the case of all other scourges sent from heaven some explanation of a cause might be given by daring men, such as the many theories propounded by those who are clever in these matters, for they love to conjure up causes which are absolutely incomprehensible to man…. But for this calamity, it is quite impossible either to express in words or to conceive in thought any explanation, except indeed to refer it to God… It started from the Egyptians who dwell in Pelusium. —Procopius, History of the Wars, II, xxii

BY THE MIDDLE of the sixth century Pelusium was more than a thousand years old, a fortress town built at the mouth of the easternmost branch of the Nile by the Persians on the site of their victory over the Egyptians in 525 B.C.E. The place was old even then. Under its original Egyptian name, Sa’ina—in English, the Wilderness of Sin—it appears in the second book of the Old Testament at both the beginning and the end of the Exodus, first as the site where God gave the Israelites manna for their hunger, and last as the place from which Joshua sent his spies into Canaan. Pelusium had later been conquered by Julius Caesar, and watched the escape of Hannibal to Rhodes. The frontier city had seen Pontius Pilate sailing east on his way to Judea, and the Jews going west on their journey into exile.

But it had never witnessed anything like the corpses. Not, to be sure, that dead bodies were a novelty in a time when a man who lived past his fortieth year was considered fortunate, and one child in four never celebrated a first birthday. Disease, even mortal disease, was nothing new, in Egypt or anywhere else. Even so, the corpses did have a distinctive feature, the grapefruit-sized swellings in groin and armpits that were called, in Greek, buboes.

The disease that appeared in Pelusium in the 540th year of the Common Era was lethal—seven in ten victims died within a week—but it was containable. Like a house fire in the middle of a desert, and in fact like every earlier disease outbreak in human history, the pestilence would soon burn itself out for lack of fuel…or, it would have but for one thing. One hundred and sixty miles to the west of Pelusium, on the other side of the Nile delta, was its much larger cousin, Alexandria. Its proximity had enormous consequence. Once the pestilence migrated across the delta, it found a huge new fuel source in the hundreds of thousands of residents of the Mediterranean’s second largest city. And, far more dangerously, it found the ships.

The ships that entered and departed the harbor of Alexandria each day were of all types. Some were galleys, moved by banks of oars. Others were wind-powered, sometimes with square sails, sometimes rigged with the triangular lateen that could be used to sail before the wind. There were tiny boats that displaced less than fifteen tons used for the coasting trade, grain ships of several hundred tons, and giants of more than a thousand tons, specially built to carry the giant obelisks used for monuments.1 The ships of Alexandria knit the world’s greatest empire together, carrying grain from Egypt to Apulia, and copper from Cyprus to Spain. A bishop in Gaul could anoint a novitiate with oil from the olive orchards of Greece, bless the event with wine from the vineyards of Italy, and celebrate the sacrament with bread baked with the wheat of Africa while wearing a garment made by Syrian weavers from Chinese silk, all because of the ships.

In the year 540, the ships that meant life to the great trading cities of the Mediterranean littoral left Alexandria as they had for centuries, carrying freight, crew…and rats, which carried a cargo of their own.

On a morning in the spring of 542, on the opposite shore of the Mediterranean from Pelusium, the most powerful man in the world greeted the dawn. Ruling the world’s richest and greatest empire was a job without end, and so it had become his custom to work straight through the night, foregoing food and sleep. The man’s work habits had convinced his enemies that he was not a man at all, but a demon requiring no rest. They whispered that he was a headless monster that prowled the halls of his palace and the streets of his city while honest people slept, a demon whose appetite demanded more souls than there are grains of sand on the beach. The ruler’s ambition had carried him from a Balkan peasant village to the peak of the known world, and was not yet satisfied. Nor would it be until his domain had regained the extent enjoyed under his predecessors.

Within months, the ships would arrive, carrying a real demon. The collision between demon and peasant-turned-ruler would mark the end of one world, and the beginning of another. Along the way, it would consume at least twenty-five million human lives.(Pg.11)


The Three Thousand-Body Problem

THE LAW of gravitation discovered in the seventeenth century by Isaac Newton states that two bodies attract each other with a force that is directly proportional to the centers of the bodies’ mass, and inversely proportional to the square of the length of a straight line separating one from the other. What this means, in practice, is that the measure of the path followed by any two bodies—the earth and the moon, for example—has a single solution, depending on the size of the respective bodies, and their distance from one another. Solutions to such two-body problems, as they are known, are simple, elegant, and most of all, unique.

Add even one more body to the system, however, and the solution is no longer unique. The best solutions to three-or-more-body problems, in fact, are “only” approximations…though, with the help of powerful computers, those approximations can be extremely precise. Calculating the path of an Apollo spacecraft from the east coast of Florida to the Sea of Tranquility, for example, which must take into account the mass of the earth, the moon, the sun, as well as the spacecraft itself (not to mention relatively minor effects exerted by other planets, comets, stars, and so on), is considerably harder than figuring the path of a dozen billiard balls on a felt tabletop, but the approximate solution has clearly been a satisfactory one.

The forces that transformed the Mediterranean world of late antiquity into medieval Europe were considerably greater in number than the significant gravitational forces acting on Apollo II, and any history that proposes a precise account of their interactions is bound to be, in some respects, unsatisfactory. These forces include, in no particular order, the geography and climate of the Mediterranean and surrounding territories; the eastward shift of the Roman empire from its Italian home to Asia Minor; the resulting westbound migrations of numerous peoples—preeminently the Goths—from the Black Sea region into the Italian and Iberian peninsulas; and the encounter with successive waves of nomadic horse archers emerging out of the Eurasian steppe (whose presence initiated a series of military innovations that led to the armed, armored, and stirruped cavalry of the European Middle Ages). Other forces, no less powerful, acted directly on the minds of the peoples of the Mediterranean: the centuries-in-refinement philosophy of Plato, particularly as seen in the late antiquity development retrospectively known as Neoplatonism; messianic Christianity, with all its attendant and perhaps inevitable, doctrinal disputes; and the growth of powerful educational institutions drawing on both traditions, whose pupils rose to the highest positions in government.

Some of the forces were initiated by individuals: the military revolution of Diocletian, the adoption of Christianity as a state religion by Constantine, and the reenergizing of the Persian Empire—and its state religion, Zoroastrianism—by its great ruler, Khusro Anushirvan all changed the path of history to greater or lesser degree. Some of the forces exerted influence in the most unlikely ways; one of the consequences of the theft of the secret of silk making from China was the withdrawal of Rome and Persia from the Arabian peninsula, only a decade before the birth in Mecca of the founder of the world’s last great monotheistic religion…one whose armies would destroy the Persian Empire and conquer most of Rome’s.

The orbital path of an object in a two-body system, or, at least, one with only two gravitationally significant bodies, is a regular one: an ellipse. To know the position and speed of such an object at a specific moment in time makes it possible to determine its position at any subsequent moment. A three-body problem—call it a three thousand-body problem—is different. In a three thousand-body system like the sixth-century Mediterranean, even knowing the status of a given object at two such moments—the first dominated by Rome and Persia, Plato and Christ, Athens and Jerusalem; the second by Islam and Christendom, Muhammad and Aquinas, Baghdad and Cologne—tells little of the route that the object followed to get from one to the other.

Though a precise retracing of the journey is impossible, however, some approximations are better than others, else the writing of history itself would be impossible. It is not necessary to argue that any single phenomenon gave birth to the nation-states of Europe to find merit in examining the moment of their conception. This moment, a hinge time if ever there was one, has historically been the century that occupies the last chapter in books on the classical world, or the world of antiquity…or, contrariwise, the first chapter in histories of the medieval world. It is the century, and the moment, when the last Roman emperor who deserves to be called great embarked on the reconquest of Italy, Spain, and North Africa; put his entire weight behind the reconciliation of schism in the Christian episcopate; and drew on the esthetic and intellectual capital of the great achievements of both the eastern and western Mediterranean world to build some of the world’s greatest architectural and legal edifices. And it is the moment, with the emperor at the absolute zenith of his achievement, that the world encountered the first pandemic in history.

The coincidence of timing does not, of course, prove that the pandemic caused Rome to fall, or Europe to be born; as above, the uncertainties of the three thousand-body problem makes such a claim fundamentally uncertain. However, the Plague of Justinian, to give both pandemic and emperor their names, killed at least twenty-five million people; depopulated entire cities; and depressed birth rates for generations precisely at the time that Justinian’s armies had returned the entire western Mediterranean to imperial control and only decades before Muhammad’s followers emerged out of Arabia to conquer Egypt, Palestine, Syria, Libya, Persia, Mesopotamia, and Spain. It is therefore as difficult to plot a course to modern Europe without acknowledging the presence of Justinian and the plague as it would be to send a satellite to the moons of Saturn without accounting for the gravitational impact (the technical word is perturbation) of the planet Jupiter.

Gravitational perturbation has proved a most useful tool to astronomers, most famously in 1846, when some twitchiness in the orbit of the visible planet Uranus was ascribed to the gravitational mass of the not yet visible planet Neptune. So, too with human history. When two nations share a similiar historical position at the same point in time, and their paths subsequently diverge, it’s worth searching for some powerful if unseen gravitational mass. Consider the cases of Rome and China.

During the fourth century of the Common Era, both great Eurasian empires were threatened with permanent dissolution. The empires founded by Augustus in 31 B.C.E. and Shih huang-ti in 221 B.C.E. each faced invasion by peoples termed “barbarians” and had, as a result, suffered significant reductions in imperial size, wealth, and even legitimacy…so much so that by the sixth century, the respective rulers of each empire embarked on a planned reconquista.

And each emperor succeeded, at least initially. In China, Yang Chien was successful in reasserting imperial authority over that portion of northern China that had, two centuries earlier, fallen to the barbarians known to historians as the Sixteen Kingdoms. And, from his capital in Asia Minor, an unlikely place from which to rule an empire still called Roman, Justinian the Great defeated, in order, the Vandals, Ostrogoths, and Visigoths, reconquering North Africa, Italy, and a fair bit of Spain.

But while the first acts of the Chinese and Roman reunification dramas were similar, their denouements were wildly different. The T’ang dynasty, which succeeded the Sui dynasty founded by Yang Chien, reigned over a united China until the tenth century. Over the same period of time, Justinian’s successors were not only unable to maintain imperial authority over Italy and Spain but also lost Egypt, Syria, the Balkans, North Africa, and Mesopotamia. While the T’ang emperors ruled all of China, the Roman Emperor—he was still called nothing else—ruled over little more than Greece and the city of Constantinople. The modern world would be dominated by the technological and military ambitions of the European nations that replaced the Roman superstate.

Why did China not atomize into half a dozen different kingdoms separated by language, as happened in Europe? The differences between the two are, of course, massive, from geography to technological developments to religious history, and most of them are far beyond the scope of this book. The simplest explanation, during the period when Rome dissolved and China coalesced, was the growth of the Islamic Caliphates, against which Christendom (as Europe was then known) was obliged to define itself. (Though, as H. L. Mencken supposedly said, “For every complex problem there is a simple solution…and it is wrong.”) Since even the prospect of a powerful enemy was insufficient to unite Europe, insufficient to keep Spain and England and France from finding their separate national identities, the forces of atomization must have been even more powerful. The obvious inference is that a common sovereign is a far more effective force for union than a common enemy, and the absence of that sovereign—the absence of Imperial Rome—permitted the pieces of Europe to define themselves based on local, rather than universal, characteristics.

The act of definition continues today. The modern political entity known as Europe—the one attempting, with limited success as of this writing, to establish a continent-wide legal charter—is a creation of imagination as much as one of geography. More so, in fact; the geography of “Europe” is a matter that has confounded historians from Herodotus to the present. In at least three different places in his great history of Justinian’s reign, Procopius attempts to define Europe by its geographical boundaries…and, like everyone else, runs aground in the east. The decision to separate Europe from Africa (Procopius called it Libya) at Gibraltar is both historically and geographically obvious. The line separating Africa from Asia at the Nile is at least defensible (though problematic, given the presence of Egyptians on both banks of the boundary for millennia). But selecting the boundary line between Europe and Asia is daunting on both geographical and historical grounds; Procopius offers two rivers feeding into the Black Sea: the Tanais (Don) and Phasis (Rioni) rivers. The Phasis appeals not only because of its topography but because of its appearance in the foundational myth of European-Asian conflict, that of Jason’s search for the Golden Fleece, the preface to the Trojan War. The modern bureaucrats wrestling with the possibility of a European Union containing both Turkey and Ukraine walk in the steps of historians dead for fifteen centuries.

Even for Procopius and his contemporaries, Europe had been a problematic idea for millennia. The earliest appearance of the term is literally mythic: Zeus’s abduction of Europa from her home in her father’s kingdom of Tyre, with her subsequent rape and abandonment on the shores of the European continent. (Herodotus’s version has Cretan merchants abducting her for their king Asterius1) Subsequent myths defined Europe as a people engaged in armed conflict with “Asiatics,” beginning with Thermopylae and climaxing retrospectively in Virgil’s epic of the departure of Aeneas from Asia to found Rome, which in turn founded “Europe.”

Both the “Europe” of myth and the Europe of the Greco-Roman world were really the world of the Mediterranean, the center of the world to historians as diverse as Fernand Braudel, G. F. W. Hegel, and Henri Pirenne, who was the first to argue, in Mohammed and Charlemagne, that the end of antiquity was marked by the Islamic invasions of the seventh century…invasions that are a direct consequence of the events related in Justinian’s Flea. The thousand-year-long transformation of a Mediterranean superstate into a northern European collection of nation-states by the time of the Treaty of Westphalia in 1648, may seem, in retrospect, inevitable. It is anything but. The idea of political entities, supreme within their own borders, entitled to something called sovereignty and defined by geography, language, and common descent, is not an exclusively European creation, but nearly so. Such nation-states did not—could not—come into being so long as the dominant political structure of the day was Rome’s empire, membership in which depended not upon birthplace or birth parents, but on acceptance of Roman authority and Roman law.

A thousand threads connect “Rome” with “Europe,” and Justinian’s Flea is therefore a book of connections: an attempt to place in context a moment in history by weaving a tapestry out of the threads that connect it to the world that replaced it. Some of those threads are technological, some military, some geographic. They include evolutionary microbiology, architecture, animal ecology, jurisprudence, theology, and even commerce. To follow any of these threads is to take a journey out of one world and into another.

These different threads, however, can be easier to follow than to weave. The goal of any history, it seems to me, is to present a picture that embraces both the exotic and the familiar—that shows a moment in time as both similar to the reader’s own, and fundamentally different. To accomplish this with Justinian’s world requires both an account of the forces that affected the late Roman empire—impersonal trends like demography and climate, human creations from armies to ideas—and the forces that the late empire exerted on the European nations that succeeded it. Doing justice to both means appreciating the historical circumstances into which Justinian was born, the legacy he left behind, and the monumental and contingent accidents that accompanied him along his journey.

Consequently the structure of this book—the warp and weft of the tapestry promised above—is divided into four parts. Part I, “Emperor,” describes the westward “barbarian” migrations as a reaction to the great eastward move of the newly Christian empire from Rome to Constantinople, each pivoting on the Balkans, the birthplace of Constantine, Diocletian, and Justinian. “Glory,” Part II, is an account of Justinian’s triumphs as they influenced the formation of the nations, the law, and the architecture of medieval Europe, and is therefore an appreciation of his contributions as a conqueror, as a jurist, and as a builder. In Part III, “Bacterium,” the other great player in the drama of the end of late antiquity appears: bubonic plague, its evolution, and its horrific impact. “Pandemic,” the fourth part, follows the journey of the plague to Persia, France, Britain, and Italy, and, equally important, visits the territories where the plague’s absence had an equally profound effect: China and Arabia.

This book began with a belief that the European history that occupies such a large part of the knowledge of every educated person was a contingent history, one that could have taken some very different turns. Nothing learned in the course of its writing has suggested precisely where those turns might have taken Europe, but it has taught a new respect for the Roman world that preceded it. Justinian’s reign, typically, displays the well-known Roman genius for soldiering and administration; it also, perhaps instructively, is an object lesson in how the world’s greatest military power can find military victories undone by local insurgencies. But in some ways, the Roman quality that appeared most admirable was a surprising one: Roman openness. It should not, in retrospect, have been so surprising to discover that Rome was such a socially mobile place. During the period of this book, the Roman Empire was ruled by an emperor who was himself born a peasant, and an empress who was a onetime courtesan, neither of whom ever set foot in Rome itself, or even Italy.

It should not, in retrospect, have been so surprising to discover that Rome was such a socially mobile place. During the period of this book, the Roman Empire was ruled by an emperor who was himself born a peasant, and an empress who was a onetime courtesan, neither of whom ever set foot in Rome itself, or even Italy.

Examples of the assimilative genius of Rome still have the power to surprise; of the great nations of history, only three—significantly, given the compass of this book, the first two are Imperial China (Li Po, the greatest poet of T’ang China, was an ethnic Turk) and Golden Age Islam; the other notwithstanding a robust tradition of nativism, is the United States of America—rival Rome in ease of entry. One cannot simply decide to become German, or Russian, or Korean in the way that one could become Roman. But even slaves could, and frequently did, become Romans, since Rome vested the right of manumission in every slave owner, and defined it as not merely freedom, but citizenship. While imperial Rome—autocratic, militaristic, arrogant Rome—is scarcely the Kingdom of Heaven, given the horrors of the blut-und-böden states that replaced it—Crusades, Inquisition, Holocaust, Gulag—one might, perhaps, be forgiven some wistfulness at its passing.

And, perhaps, some wonder at the possibility that that passing was hastened by the bite of a flea. (Pg.8)

“Justinian’s Flea: The First Great Plague and the End of the Roman Empire” by William Rosen.