If you answered Pittsburgh, you are right. As a major source of steel products and technology, Pittsburgh and southwestern Pennsylvania were once a powerful hub of the Industrial Age -- one that pushed the United States to world leadership as an industrial giant.

Pittsburgh steel was used to build some of the most important structures of the modern age: the Brooklyn Bridge, the Panama Canal locks, the Empire State Building, Rockefeller Center, the Oakland Bay Bridge, and the United Nations. During World War II, southwestern Pennsylvania became known as America's "Arsenal of Democracy," because its mills were working around the clock to make enough steel for America and its allies. Andrew Carnegie (see the "Amazing Americans" section of this Web site) became the richest man in the world because of his ownership of steel mills.