Once established, these two huge imperial systems shared a number of common features. Both, for example, defined themselves in universal terms. The Roman writer Polybius spoke of bringing “almost the entire world” under the control of Rome, while the Chinese state was said to encompass “all under heaven.” Both of them invested heavily in public works—roads, bridges, aqueducts, canals, protective walls—all designed to integrate their respective domains militarily and commercially.

Furthermore, Roman and Chinese authorities both invoked supernatural sanctions to support their rule. By the first century C.E., Romans began to regard their deceased emperors as gods and established a religious cult to bolster the authority of living rulers. It was the refusal of early Christians to take part in this cult that provoked their periodic persecution by Roman authorities.

In China, a much older tradition had long linked events on Earth with the invisible realm called “Heaven.” In this conception, Heaven was neither a place nor a supreme being, but rather an impersonal moral force that regulated the universe. Emperors were called the Son of Heaven and were said to govern by the Mandate of Heaven so long as they ruled morally and with benevolence. Peasant rebellions, “barbarian” invasions, or disastrous floods were viewed as signs that the emperor had ruled badly and had thus lost the Mandate of Heaven. Among the chief duties of the emperor was the performance of various rituals thought to maintain the appropriate relationship between Heaven and Earth. What moral government meant in practice was spelled out in the writings of Confucius and his followers, which became the official ideology of the empire (see Chapter 4).

Both of these second-wave civilizations also absorbed a foreign religious tradition—Christianity in the Roman world and Buddhism in China—although the process unfolded somewhat differently. In the case of Rome, Christianity was born as a small sect in a remote corner of the empire. Aided by the pax Romana and Roman roads, the new faith spread slowly for several centuries, particularly among the poor and lower classes. Women were prominent in the leadership of the early Church, as were a number of more well-to-do individuals from urban families. After suffering intermittent persecution, Christianity in the fourth century C.E. obtained state support from emperors who hoped to shore up a tottering empire with a common religion, and thereafter the religion spread quite rapidly.

In the case of China, by contrast, Buddhism came from India, far beyond the Chinese world. It was introduced to China by Central Asian traders and received little support from Han dynasty rulers. In fact, the religion spread only modestly among Chinese until after the Han dynasty collapsed (220 C.E.), when it appealed to people who felt bewildered by the loss of a predictable and stable society. Not until the Sui (sway) dynasty emperor Wendi (r. 581–604 C.E.) reunified China did the new religion gain state support, and then only temporarily. Buddhism thus became one of several alternative cultural traditions in a complex Chinese mix, while Christianity, though divided internally, ultimately became the dominant religious tradition throughout Europe (see Chapters 8 and 10).

The Roman and Chinese empires also had a different relationship to the societies they governed. Rome’s beginnings as a small city-state meant that Romans, and even Italians, were always a distinct minority within the empire. The Chinese empire, by contrast, grew out of a much larger cultural heartland, already ethnically Chinese. Furthermore, as the Chinese state expanded, especially to the south, it actively assimilated the non-Chinese, or “barbarian,” people. In short, they became Chinese, culturally, linguistically, and through intermarriage in physical appearance as well. Many Chinese in modern times are in fact descended from people who at one point or another were not Chinese at all.

The Roman Empire offered a different kind of assimilation to its subject peoples. Gradually and somewhat reluctantly, the empire granted Roman citizenship to various individuals, families, or whole communities for their service to the empire or in recognition of their adoption of Roman culture. In 212 C.E., Roman citizenship was bestowed on almost all free people of the empire. Citizenship offered clear advantages—the right to hold public office, to serve in the Roman military units known as legions, to wear a toga, and more—but it conveyed a legal status, rather than cultural assimilation, and certainly did not erase other identities, such as being Greek, Egyptian, or a citizen of a particular city.

Various elements of Roman culture—its public buildings, its religious rituals, its Latin language, its style of city life—were attractive, especially in Western Europe, where urban civilization was something new. In the eastern half of the empire, however, things Greek retained tremendous prestige. Many elite Romans in fact regarded Greek culture—its literature, philosophy, and art—as superior to their own and proudly sent their sons to Athens for a Greek education. To some extent, the two blended into a mixed Greco-Roman tradition, which the empire served to disseminate throughout the realm. Other non-Roman cultural traditions—such as the cult of the Persian god Mithra or the compassionate Egyptian goddess Isis, and, most extensively, the Jewish-derived religion of Christianity—also spread throughout the empire. Nothing similar occurred in Han dynasty China, except for Buddhism, which established a modest presence, largely among foreigners. Chinese culture experienced little competition from older, venerated, or foreign traditions. It was widely recognized across much of East Asia—in Japan, Korea, and Vietnam, for example—as the model to which others should conform.

Language served these two empires in important but contrasting ways. Latin, an alphabetic language depicting sounds, gave rise to various distinct languages—Spanish, Portuguese, French, Italian, Romanian—whereas Chinese did not. Chinese characters, which represented words or ideas more than sounds, were not easily transferable to other languages. Written Chinese, however, could be understood by all literate people, no matter which spoken dialect of the language they used. Thus Chinese, more than Latin, served as an instrument of elite assimilation. For all of these reasons, the various peoples of the Roman Empire were able to maintain their separate cultural identities far more than was the case in China.

Politically, both empires established effective centralized control over vast regions and huge populations, but the Chinese, far more than the Romans, developed an elaborate bureaucracy to hold the empire together. The Han emperor Wudi (r. 141–87 B.C.E.) established an imperial academy for training officials for an emerging bureaucracy with a curriculum based on the writings of Confucius. This was the beginning of a civil service system, complete with examinations and selection by merit, which did much to integrate the Chinese empire and lasted into the early twentieth century. Roman administration was a somewhat ramshackle affair, relying more on regional aristocratic elites and the army to provide cohesion. Unlike the Chinese, however, the Romans developed an elaborate body of law, applicable equally to all people of the realm, dealing with matters of justice, property, commerce, and family life. Chinese and Roman political development thus generated different answers to the question of what made for good government. For those who inherited the Roman tradition, it was good laws, whereas for those in the Chinese tradition, it was good men.

Finally, both Roman and Chinese civilizations had marked effects on the environment in various ways. The Roman poet Horace complained of the noise and smoke of the city and objected to the urban sprawl that extended into the adjacent fertile lands. Roman mining operations, the smelting of metals, its large-scale agriculture, and its growing population—all of this led to extensive deforestation and consequent soil erosion. The shortage of wood in the heartland of the empire led to the relocation of some ceramic workshops to Gaul, where timber was more plentiful. Lead pollution, derived from the smelting of lead ores in open furnaces and from lead water pipes and cooking pots, shows up in the bones of Roman burials and in bones found as far away as Greenland, where studies of the icecap indicate that lead in the atmosphere increased during Roman times. Here is perhaps the earliest example of international atmospheric pollution.

Large-scale Chinese ironworking during the Han dynasty likewise contributed to substantial urban air pollution, while a rapidly growing and dense population practicing intensive agriculture stripped the North China plain of its ancient forest cover, causing sufficient soil erosion to turn the Hwang-ho River its characteristic yellow-brown color. What had been known simply as “the River” now became the Yellow River, which frequently flooded with devastating results and over many centuries dramatically changed course. In addition, as China expanded north and west into the steppe lands of the pastoral peoples, military/agricultural colonies of Chinese farmers turned pasturelands into farmlands, plowing up long-established sod. When the Chinese state subsequently grew weaker or actually collapsed, such farms were abandoned, wind erosion took hold, and deserts emerged.14