The metal-framed building transfers loads to a skeleton of columns and beams so that exterior walls carry only themselves, freeing the facade. William Le Baron Jenney's Home Insurance Building in Chicago (1885) is usually cited as the first tall building with a largely metal frame. By the mid-twentieth century the frame supported a non-structural 'curtain wall' of glass and metal hung from the floor edges, as in Lever House (1952) and the Seagram Building (1958) in New York. This separation of structure and skin defined the modern office tower.
The steel frame and curtain wall made the tall building and the glass office tower possible, reshaping skylines and central-business-district land values.