The development of the steel frame, which became a crucial aspect of Modern architecture, had its roots in the iron frames that began to make their appearance in the tall office buildings of Chicago in the 1880s. Until that time, almost all buildings of any size including all masonry buildings had depended on their walls to hold them up; the material of the walls both kept the weather out and formed the structure of the buildings. The taller the building was, the thicker the walls had to be at the base to support the vast weight above them . There is a limit to how tall such a building can practically be before the lower floors begin to disappear in the thickness of the walls; the tallest load-bearing masonry office building ever built was Chicago’s Monadnock building in 1893, at seventeen storeys high and with walls six feet thick at the base. But with the development of the steel frame, the walls were no longer required to bear any weight; instead, the building was held up ...