The tall building radically reshaped the modern city, thrusting it upward in the decades around the turn of the 20th century, just as the automobile pushed it outwards between the world wars. The skyward trend began in the 1890s, when high-rise commercial buildings began replacing the six- and seven-story structures that lined the downtown streets of U.S. cities, overtaking churches as those cities' tallest buildings and as the key reference points on the skyline. The symbolism is (and was) clear -- in America, a nation founded by devout pilgrims, commerce was overtaking faith as the pivot of urban life.

The breakthrough was the advent of two new technologies: the steel structural frame and the elevator, the former making tall buildings possible and the latter making them practical.

The 10-story Home Insurance Building (1885) in Chicago, designed by William LeBaron Jenney, was the first tall building to be supported by a steel frame -- it weighed only one-third that of an equivalent masonry structure. Jenney's building was the first high-rise to have large windows -- a feature that would become a key characteristic of modern skyscrapers.