In the year these images were published, a century ago, an equal number of people in America lived in the cities and in the countryside. But by the end of the decade the urban population was larger, as farms replaced horses and laborers with machines and farmhands and their families moved to the cities to work in factories that paid more than they could earn as agricultural laborers.

From photographs, art and movies we have some idea of the extremes of city living (then and now!). In New York, for instance, we can see the squalid slums photographed by Jacob Riis, and we can peek in on the opulent life of Gilded Age industrialists (robber barons?) such as Andrew Carnegie, whose extravagent mansion is now the Cooper-Hewitt National Design Museum. But the vast majority of people living in cities with large and dense populations relied heavily on technology to enable them to live and work comfortably or even tolerably. Housing, transportation, electricity grids, water supplies, sewer systems—these made up the body of modern city life.

Our slide show here is a small peek into the vast complexity of the urban engineering that goes into helping a city survive and thrive. For a more complete look at the growth in the technology over the past 170 years, our Scientific American Archive is available for purchase here: www.scientificamerican.com/magazine/sa