Willis Tower

Still "the Sears Tower" to most of the city, Willis Tower was the tallest building in the world from its completion in 1973 until 1998, and remained the tallest in the United States for decades after. Its engineer, Fazlur Rahman Khan, built it as a bundle of nine square "tubes" rising together off a common base — the tubes stop at different heights, which is what gives the tower its stepped, setback silhouette. The design let it go higher with less steel than anything before it, and it changed skyscraper engineering worldwide.

Photographed June 2024. The stepped profile is unmistakable from the right angle — the nine tubes dropping away at staggered heights toward the top. In black and white the building becomes pure structure: the diagram of how it stands, written into its shape.