Welder on Sears Tower, 1973

Seemingly oblivious to the height or the view, a welder works near the top of the 110-story Sears Tower in 1973. (Bill Yates, Chicago Tribune)

Several thousand employees gathered outside the soaring Sears Tower for a topping-out ceremony that would see a 2,500-pound steel girder bearing 12,000 signatures hoisted more than a quarter-mile into the sky. It was now the tallest building in the world.The ceremony had been anticipated since the company's decision in 1970 to move its headquarters from Homan Avenue on the West Side. To the city's relief, the new location would not be in the suburbs but at Wacker Drive and Jackson Boulevard, on the western edge of downtown Chicago.

"I want to thank (Sears) for staying in Chicago when so many are leaving," Mayor Richard J. Daley said.

Three months later, Sears would begin moving its employees into what became known as a "vertical city," 15,000 people working, shopping and dining inside one building. Architect Bruce Graham and engineer Fazlur Khan designed the 110-story tower as a bundle of nine square tubes, seven of which end at either the 50th, 66th or 90th floors, mainly to reduce the wind load on the upper stories. Only two of the nine squares reach the full 1,454-foot height of the building.

For 23 years, the tower reigned as the world's tallest building, but in 1996, the Petronas twin towers in Kuala Lumpur, Malaysia, surpassed it by 29 feet.

In July, however, the architectural group responsible for naming the Petronas towers the world's tallest, threw Sears Tower a bone. Sears, it said, had the world's tallest roof and the highest occupied floor.

Before it ceded its lofty title, the tower's stature had slipped in a different way: Sears--no longer the world's largest retailer--began moving to a new location in Hoffman Estates in 1992.