Pittsburgh is also called the "Steel City," due to its rich history as a center of the steel industry. Steel production formed the basis of the city's growth and prosperity beginning in the 19th century and continuing into the 1970s. Steel mills were once the main employers of many Pittsburgh residents, and much of that legacy is still evident in the local culture.
The rise of the Pittsburgh steel industry began in earnest when entrepreneur Andrew Carnegie opened the Edgar Thomson Works mills in 1875 and began mass-producing durable, inexpensive steel through the patented Bessemer process. His company later became part of the larger U.S. Steel Corporation, which produced a significant percentage of the nation's steel during its heyday. Both Carnegie and Henry Clay Frick are still remembered for their substantial economic and philanthropic contributions to the steel city.
Pittsburgh history also attributes the growth and diversity of the steel city and its surrounding boroughs to large rates of immigration that coincided with the success of the steel mills. Newcomers from other countries frequently passed through New York's Ellis Island and ventured to Pennsylvania in search of jobs at the many steel manufacturing industrial sites. The highest volume of Pittsburgh-produced steel products topped 95 million during the Second World War.
The steel city faced a significant economic downturn beginning in the 1980s when the majority of Pittsburgh's steel plants were forced to close or outsource production to other regions. Before the end of the decade, only two steel plants remained in the surrounding area. Wheeling-Pittsburgh Steel is one of the few steel manufacturing plants with all of its operating facilities still in this section of western Pennsylvania. The steel city has since become economically revitalized due to a good deal of industry diversification. Some of the largest Pittsburgh employers are now within the financial and technology sectors.
Pittsburgh is also sometimes known as the "city of bridges" due to the prominent group of bridges that span the Allegheny River to the north and the Monongahela River to the south, providing easy access from the boroughs to the downtown area. Each bridge required significant local steel fabrication at the time of construction, a source of pride for many Pittsburgh natives. Lifelong residents in fact take such pride in the legacy of the steel industry that the championship-winning Pittsburgh Steelers football team even takes its name from this city history.