This is curtain-wall modernism in full stride. The project was commissioned by developer Herbert S. Greenwald, Mies’s early and influential client, whose death in 1959 halted development of two additional towers planned for the site. The glass-and-aluminum skin is suspended in front of the columns, which comprise two different structural systems (reinforced concrete on the lower floors and steel above). The space between the columns and the skin contains vertical ventilation shafts, allowing for more efficient heating and cooling than in Mies’s previous buildings.