In the 1970s, Chicago skyscrapers exploded in scale, innovation, and technological sophistication. Two seminal buildings of this period appear side by side in this rendering of North Michigan Avenue—the John Hancock Center (1970) and Water Tower Place (1976). Designed by architect Bruce Graham and engineer Fazlur Kahn of the architecture firm Skidmore, Owings & Merrill, the muscular black frame of the John Hancock Center expresses its trussed-tube system, a new engineering concept that allowed the rise of supertall towers while advancing a distinctive structural aesthetic. Water Tower Place, shown in a preliminary two-tower version in the foreground, advanced a different kind of innovation—a new form of mixed-use skyscraper that joined a large retail mall and parking with office space and residential units, transferring formerly suburban functions to the city center.