About the image
Unity Building under Construction, Industrial Chicago, 1892. Chicago History Museum, ICHi-23088.

The most important development in skyscrapers was the evolution of steel frame construction.

Previously, masonry walls bore a building’s weight. Now, the glass, brick, and terra cotta “hung” on the steel skeleton like a curtain as the columns distributed the weight across the foundation. To make buildings fireproof, engineers clad the steel with terra-cotta tiles. These buildings weighed less than their masonry counterparts, so the sky was literally the limit.

But the “light” appearance of these buildings was also a deterrent, as some people felt reassured by the thickness of masonry walls.

© 2012 John D. and Catherine T. MacArthur Foundation