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.
^O. Chanute and George Morison, The Kansas City Bridge with an account of the Regimen of the Missouri River and a Description of the Methods used for Founding at the River, D. Van Nostrand, NY, 1870, Michigan Historical Reprint Series, University of Michigan