Chicago is generally considered by historians to be the birthplace of the skyscraper. Opened in 1884, the 10-storey Home Insurance Building was the first building to use structural steel. Though demolished in 1931, its legacy lives on through other record-breaking skyscrapers across the city. Chicago is home to an impressive collection of architecture and tall buildings, boasting four skyscrapers whose roof heights surpass the 300-metre supertall designation. Another two break that threshold when their spires are considered. As the third largest city in the United States, Chicago's iconic skyline is naturally symbolized by a dense cluster of towers, a skyline which could have been even more defining if the visionary 7 South Dearborn was realized.

Chicago's Willis Tower, image by Marcus Mitanis

The concept was conceived by Scott Toberman of European-American Realty in 1999. He proposed a 478-metre (1,567-foot) tower for the corner of Madison and Dearborn Streets. At that height, it would have surpassed both the Petronas Towers and the Willis Tower — then known as the Sears Tower — to become the tallest building in the world. Three 132-metre (433-foot) broadcast antennas would bring the total height above 600 metres to an even 2,000 feet.

7 South Dearborn, image via Adrian Smith + Gordon Gill Architecture

Designed by Adrian Smith, who at the time worked for Skidmore, Owings & Merrill, the building's stayed mast structural system provided the necessary platform to rise to such an extravagant height. A series of recessed spaces emanating from the central core interrupted the vertical volume. The building featured column-free office spaces on 36 floors and 40 floors containing 360 residential units. Communication facilities ultimately comprised 13 floors, while an additional 12 floors were set aside for parking use.

7 South Dearborn, image via Adrian Smith + Gordon Gill Architecture

The 18-storey First Federal Building, which once housed the offices of the Chicago Tribune newspaper, was demolished in advance of construction. Though the proposal received approval from the City, it never came to pass. Financing for the tower's construction was not secured and the plan was shelved in 2000. The site is now home to a building much smaller in scale, the 39-storey One South Dearborn, which was completed in 2005 by Hines.

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