<P> Although American downtowns lacked legally - defined boundaries, and were often parts of several of the wards that most cities used as their basic functional district, locating the downtown was not difficult, as it was the place where all the street railways and elevated railways converged, and--at least in most places--where the railroad terminals were . It was the location of the great department stores and hotels, as well as the theatres, clubs, cabarets, and dance halls, and where skyscrapers were built once that technology was perfected . It was also frequently, at first, the only part of a city that was electrified . It was also the place where street congestion was the worst, a problem for which a solution was never really found . </P> <P> But most of all, downtown was the place where the city did its business . Inside its small precincts, sometimes as small as several hundred acres, the majority of the trading, selling, and purchasing--retail and wholesale--in the entire area would take place . There were hubs of business in other places around the city and its environs, but the downtown area was the chief one, truly the central business district . And as more and more business was done downtown, those who had their homes there were gradually pushed out, selling their property and moving to quieter residential areas uptown . </P> <P> The skyscraper would become the hallmark of the downtown area . Prior to the invention of the elevator--and later the high - speed elevator--buildings were limited in height to about six stories, which was a de facto limit set by the amount of stairs it was assumed that people would climb, but with the elevator, that limit was shattered, and buildings began to be constructed up to about sixteen stories . What limited them then was the thickness of the masonry needed at the base to hold the weight of the building above it . As the buildings got taller, the thickness of the masonry and the space needed for elevators did not allow for sufficient rentable space to make the building profitable . What shattered that restriction was the invention of first the iron - and then the steel frame building, in which the building's load was carried by an internal metal frame skeleton, which the masonry--and later glass--simply hung off of without carrying any weight . </P> <P> Although first used in Chicago, the steel - framed skyscraper caught on most quickly in New York City in the 1880s, and from there spread to most other American cities in the 1890s and 1900s . The apparent lack of a height limitation of this type of building set off a fervent debate over whether their height should be restricted by law, with proponents and opponents of height limits bringing out numerous arguments in favor of their position . The question of height limits also had a profound implication for the nature of downtown itself: would it continue to be a concentrated core, or as it grew, would height limits force it to spread out into a larger area . In the short run, the proponents of height limits were successful in their efforts . By the 1910s, most of the largest and medium - sized cities had height limits in effect, with New York--despite several concerted efforts to enact them, Philadelphia, Detroit, Pittsburgh and Minneapolis being notable holdouts . </P>

The centers of most cities became business areas after the invention of what