How did a steel skeleton and a safe elevator make skyscrapers possible?

A tall building made of stacked stone has a problem that gets worse with every floor: the walls at the bottom must carry everything above them, so they have to grow absurdly thick. Without a steel frame instead of stone or brick, the lower walls of a tall building would be too thick to be practical. The fix was to stop asking the walls to hold the building up. A steel frame is a skeleton of vertical steel columns and horizontal I-beams in a rectangular grid, and the floors, roof and walls are all hung from it. That technique made the skyscraper possible.

The second ingredient was getting people up there. The invention of the elevator was a precondition for skyscrapers, because most people would not, or could not, climb more than a few flights of stairs. Early lifts had a frightening weakness: a snapped cable meant a fall. In 1852 Elisha Otis introduced a safety elevator that prevented the cab from falling if the cable broke, and in 1854 he showed it off at the New York exposition in a dramatic, death-defying presentation.

Chicago put the two together. The Home Insurance Building, designed by William Le Baron Jenney and finished in 1885, rose ten storeys and 138 feet, and is often called the world's first skyscraper. In one account, its frame carried the entire weight of the walls. The building weighed only one-third as much as a masonry building, and that alarmed city officials so much that they halted construction while they investigated its safety.

That suspicion was understandable: nobody had seen a building stand up this way. Today the question of who built the "first" skyscraper is still argued, and the frame itself is described differently by different sources, with some saying it was iron rather than steel. But the principle won, and within a few years the all-steel Rand McNally Building showed where things were heading: up.