
Even though cities were dominant politically and central to many earlier societies, only in the last century so have predominantly urban societies emerged. Before that most humans lived in villages or in hunter-gatherer bands. Everyone was in everyone else’s business. Anonymity was simply not a thing for most humans in most periods of our species’ history.

And, that ceiling is smaller than the number of people who live in close proximity to each other in cities. The potential facelessness of your neighbors in a city, and its diversity and cosmopolitanism is one reason that it was in cities that written laws displayed in public places emerged as a custom. Societies not bound together by social interaction and kinship needed abstractions which could scale. Laws, kings, and religions are just some of the cultural inventions that were essential to maintain order in a city where strangers interacted daily.
But were these cities really incubators for anonymity? I would argue that the premodern city offered far less anonymity, and therefore privacy than the modern city. Premodern cities were dense, due to limitations in transportation. They were defined by neighborhoods. Additionally, economic activities in cities were often defined by relationships between people, whether it be between a patron and an artisan, or members of a cooperative guild. In some ways, premodern cities were a collection of villages.

By the second half of the 20th century, individuals in cities could be totally self-sufficient and isolated from other human beings if they so chose when it came to personal relationships. The rationalization of modern life made deep human interaction a choice, and to some extent, privacy was the default state.
The rationalization of economic relations continues. But over the last 20 years, and especially the last ten or so, the default state of privacy has disappeared. If you know someone’s name you can usually find their age, where they have lived their adult life, who they lived with, and who their relatives are. Websites like Zillow can tell you their home-value or when/if they bought their home and for how much. Facebook, Twitter, and other social media make it so you can find out many things about a person.
Recently a friend of mine who became newly single after ten years in a relationship decided to try out online dating (for the first time). One thing he found is that you have to assume that your matches may have Googled you beforehand (presumably this depends on whether the site gives you full name or not). If you are too shy to talk to your neighbors, just look up who lives at the various addresses around you. Once you have their names you can find out everything else.

Whereas the political and social views of most employees of a corporation were out of view in the 20th-century, today many companies are snooping around in Facebook feeds and doing simple background checks. You may not have a personal relationship with a large company, but it has a relationship with the data that it defines you by.
The 20th-century was the century of privacy because the machinery of information distribution appropriate to hunter-gatherers and villages did not scale to cities. And 20th-century technology never caught up to the scale of the cities and economies of that period in terms of distributing information. As the 21st-century proceeds, it seems that information technology is finally now in place.
