Sears, Roebuck and Company commissioned the tower in 1970. When construction was completed in 1973, it surpassed the World Trade Center as the tallest building in the world. It is currently the tallest structure in the U.S., but is surpassed by the CN Tower in Ontario as the tallest freestanding structure in North America. This summer, the building will be renamed the Willis Tower.
Candice C. Cusic, Chicago Tribune