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Dunlap's Creek Bridge

Brownsville, Pennsylvania
Completed 1838

Claim to Fame: The Dunlap’s Creek Bridge is the oldest all-metal arch bridge in the United States. It demonstrated the feasibility of using cast iron in bridge construction.

 Dunlap's Creek Bridge  
 Courtesy historicbridges.org

"In some one of my communications of last fall I intimated that I had matured in my mind the plan of the Cast Iron Bridge to be constructed over Dunlap's Creek - differing in its principles of construction from any of which I could find a notice by either English or French Engineers..."
 - Capt. Richard Delafield, letter to the Chief Engineer, U.S. Army Corps of Engineers, 1836

Not only was Dunlap's Creek Bridge the first cast-iron bridge in America, it was the first metal bridge anywhere to use what its builder, Capt. Richard Delafield, U.S. Army Corps of Engineers, described as "standardized, interchangeable, manufactured parts." The bridge was built as part of the federal government's effort to make repairs on the National Road  before handing authority over to the states. Dunlap's Creek at Brownsville was an especially troublesome crossing, having destroyed three previous bridges since 1801.

But Brownsville, located on the Monongahela River, was becoming a major center for the development of steamboats that were used on the Monangahela and Ohio rivers. Leasing a steamboat foundry and purchasing high-quality, raw iron himself, Capt. Delafield proceeded to supervise every detail of fabricating a structure that has lasted more than 160 years and is still in use today. Although spanning only 80 feet and soon ignored by the majority of traffic taking to the early canals and railroads, Dunlap's Creek Bridge remains a testament to American ambition and ingenuity.

Facts
1. The five identical arch ribs that create the basic skeleton of Dunlap's Creek Bridge are composed of tubular segments that closely resemble the cylinders being made at the time for steamboat engines.
2. Dunlap's Creek Bridge was the last federal contract for the reconstruction of the eastern section of The National Road. When U.S. Route 40 was built to replace the National Road, engineers chose a path for the roadway that no longer passed through Brownsville or over Dunlap's Creek Bridge.
3. Both Capt. Delafield and his chief assistant, Lt. George Cass, were graduates of the U.S. Military Academy at West Point, founded in 1802 as an apprentice school for military engineers, and the first formal school of engineering in the U.S.
4. Capt. Delafield later became superintendent of the U.S. Military Academy at West Point, Chief of Engineers in the U.S. Army, and head of the U.S. Army Corps of Engineers. Lt. Cass organized the first steamboat company on the Monongahela, established an express company, became president of a number of railroad companies, including the Northern Pacific, and was twice the Democratic candidate for governor of Pennsylvania.
5. Sidewalks were added to the bridge in 1920, along with supports of modern steel.

Resources

1. Carl Condit, American Building Art -- The Nineteenth Century; Oxford University Press, 1960.
2. Forest G. Hills, Rails and Waterways: The Army Engineers and Early Transportation; University of Oklahoma Press, 1957.