U.S. Capitol Building Dome

The U.S. Capitol Dome, whose construction began in 1856, is made of 8,909,200 pounds of cast-iron girders, plates, columns, and ornaments. Cast iron, a ferrous predecessor of steel, was widely used for buildings in the 19th century until steel, an even stronger material, supplanted its use. As the puzzle image shows, when Abraham Lincoln was inaugurated in 1861, the massive dome was still under construction--it was finally completed in 1866.

Like the U.S. Capitol Building Dome, structural steel goes way back. Learn more about steel's enduring role in American history with AISC's Centennial timelines series.