Keystone Bridge Company  The Keystone Bridge Company, founded in 1865 by Andrew Carnegie, was an American bridge building company. It was one of the 28 companies absorbed into the American Bridge Company in 1900. The company advertised its services for building steel, wrought iron, wooden railway and road bridges. It held a patent for wrought iron bridges and also supplied wrought iron columns for buildings. Thomas Carnegie worked for Keystone Bridge as treasurer for roughly 20 years, from the founding of the company until his death in 1886. Keystone is perhaps best remembered for the Eads Bridge in St. Louis, completed in 1874, which survives to this day. A number of its works are listed on the U.S. National Register of Historic Places. Carnegie sold his company, Carnegie Steel Company to J.P. Morgan in 1901. Works include (attribution):