Sometimes these settlements were permanent, sometimes for seasonal or occasional use. Sometimes they were fairly compact, composed, for example, of small villas surrounded by gardens in a pattern we would today call suburban. In other cases they were very dispersed with imposing houses set on a large acreage, often with a conscious attempt to maintain a rural appearance. These we would call today exurban. Although this pattern apparently characterized Babylon and Ur and many of the earliest large cities known to us, the best evidence we have comes from ancient Rome. At the beginning of the Christian era, this great city had an estimated population of about 1 million people piled up within city walls that enclosed a little more than six square miles. In other words it had a population of a city like Dallas today but in less than one-fiftieth of the space. This created densities of something like 150,000 per square mile. This kind of density, which would translate to more than two hundred people per acre, seems to have characterized most large, thriving cities up until the beginning of the twentieth century. It is hard for us today even to imagine the consequences of crowding of this order in cities that had, by today's standards, primitive water delivery waste removal, and transportation services.
In Rome, as in most other cities until quite recently, this crowding was even worse than the figures suggest because social and economic inequalities were much greater than they are today. A small group of wealthy Romans lived in splendor in spacious palaces that, together with nonresidential facilities, took up most of the space within the walls. This left relatively little acreage for the neighborhoods that housed the vast majority of families. In these neighborhoods apartment blocks were built so densely that they allowed little direct sunlight or ventilation into living quarters. Human wastes disgorged from the apartments into the streets contaminated the soil and water; a vast number of fires used for heating and industrial uses polluted the air. It is not surprising that periodic epidemics wiped out large segments of the urban population. These urban plagues continued in the Western world until well into the twentieth century, and they continue to this day in some large cities in the developing world.
Despite the obvious problems, several factors made high densities in cities a necessary evil. One was the fact that most cities owed their existence to some specific geographical feature: a site along a trade route, a safe harbor, a good location for a bridge, a piece of ground that could be easily defended, a rapids that could be harnessed to provide water power. The cities that developed around these strategic points could not spread very far because of the limits of accessibility. For the wealthy, accessibility was usually not a problem because they had horses and carriages; for the poor there was only walking. This meant that until the widespread availability of inexpensive public transportation, which was a development of the late nineteenth century, most urban functions had to be located in close proximity to one another. Residential, commercial, and industrial facilities often mingled indiscriminately along the crowded streets with little consideration for the health or safety of the inhabitants. Crowding was reinforced by military considerations as well. Most large cities, at least until the nineteenth century, were walled for security reasons, and the crushing expense of building and maintaining the wall guaranteed that cities remained as compact as possible. They expanded only when the lack of space for essential urban activities became truly intolerable.
Outside the walls of Rome was what citizens called suburbium, meaning what was literally below or outside the walls. Here were land uses that couldn't be accommodated in the city. Along the roads that led out of town grew up settlements that clustered around industrial facilities, cemeteries, and businesses catering to travelers entering and leaving the city. For many suburbanites, the reason for living in the suburbs was a matter of cost. They could not afford to live in the city and so had to forgo urban services and the protection of the walls. These residents often lived in poorly built dwellings that could be even worse than those within the walls because of the lack of municipal services and the pollution generated by brick kilns, slaughterhouses, and other industries. At the opposite end of the spectrum were some of the wealthiest Romans, who could afford to maintain, in addition to their city residences, elegant villas near the sea or in the cool hills east of Rome near places like Tivoli and Frascati.
Sometimes these suburban or exurban dwellings served only as weekend houses, but for those who could afford to do so, these weekend houses often became much more than that. Ancient, medieval and early modern literature is filled with stories of the elegant life of a privileged aristocracy living for large parts of the year in villas and hunting lodges at the periphery of large cities. Nor was the preference for living quarters outside the center restricted to the Western world. Exactly the same sentiments in favor of low-density living outside the city were voiced by the gentry in China at least as early as the Ming dynasty. High density from the time of Babylon until recently, was the great urban evil, and many of the wealthiest or most powerful citizens found ways to escape it at least temporarily.
It appears that the forces that work toward increased concentration and those fueling a drive toward decentralization are, like so many other aspects of urban life, related to economic cycles. Although little is known about these cycles, it appears that throughout history, at least until recently, as most cities went through their most intense phase of early economic growth, the process of concentration tended to dominate over that of decentralization as residents from outlying areas were drawn into the city center. Then, as the economy matured, the balance shifted as the number of residents who were able to move outward to the suburbs and exurbs exceeded the number coming from the agricultural hinterland to the center.
We can use modern London as a good exemplar of these processes. Because London was the largest and economically most dynamic city in the Western world in the early modern period, it was here that these trends were most apparent. In the seventeenth and eighteenth centuries, for example, there was a vast influx of new residents both because changes in agricultural production forced thousands of families off the land and because an expanding urban job market based on new modes of industrial production lured others in. The piling up of population and commercial activities at constantly higher densities in the center, however, tended to produce a countervailing move of people out to the urban periphery.
During this period an entire new class of Londoners, flush with the profits earned in an expanding economy, was able to build or lease houses well beyond the walls of the city of London. The most important direction for affluent suburban growth was to the west, stretching in the direction of the leafy gardens of the royal palaces at Westminster and Whitehall. In this area, in what is now London's Central West End, several of the great aristocratic families developed their land as private, sometimes gated, communities with townhouses laid out around landscaped squares. Life here would have been remarkably calm, quiet, and orderly compared to that along the teeming streets of the walled city of London a mile and a half to the east. For many residents it involved what was then a long-distance commute back into the city by private carriage.
There was also suburban development to the east of the London walls but of a vastly different kind. This area accommodated large-scale warehouses and industrial facilities near the great London docklands. These industrial activities drew working-class families attached to them. The densities of these districts sometimes rivaled those within the walls. As a consequence they, like the least affluent quarters of the city of London itself, were congested, unpleasant, and unhealthy. Observers increasingly spoke of two entirely different Londons, the affluent, airy one to the west and the dark and congested one to the east. Clearly from the beginning of modern urban history, and contrary to much accepted wisdom, suburban development was very diverse and catered to all kinds of people and activities.
Beyond suburbia there was also a significant development in what we would now call exurbia, in thinly settled areas beyond the regularly built-up city and suburbs. Although much of this exurban territory often looked purely rural and agricultural, this appearance, often maintained at great expense, belied the fact that the primary economic, social, and cultural ties of the inhabitants were back to the city. Daniel Defoe, in his descriptions of Surrey in the early eighteenth century was struck by the number of houses of 'gentlemen of quality' in the villages around the city. These men were neither farmers nor members of the landed gentry. Instead their houses were 'citizen's country houses whither they retire from the hurries of business and getting money to draw their breath in a clear air, and to divert themselves and their families in the hot weather.'
This world, familiar to us from the works of authors like Jane Austen, represented a vast change in urban society. The amount of wealth required to build, staff, and maintain a country house in the Renaissance would have been beyond the reach of any but the wealthiest families in any society These houses often required entire villages to house all of the workers needed to provide the necessities of everyday life. Already by the eighteenth century, in affluent countries like Britain, a highly developed transportation and communications system made it possible for a much larger group of citizens to enjoy the pleasures of living at different times in both city and country.
The exodus of families from central London to suburbia and exurbia was offset by the continued arrival of poor newcomers from the countryside. The result was a great churning of population as both centralization and decentralization exerted their influence. Already by the seventeenth century, however, the processes of decentralization were clearly the more important.