Keystone Bridge Company

The Keystone Bridge Company, founded in 1865 by Andrew Carnegie, was an American bridge building company.

The company advertised its services for building steel, wrought iron, wooden railway and road bridges.

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 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.