There is a steel bridge across the Pee Dee River east (railroad north) of Florence, SC on CSX. Acording to the local newspaper, the large supports for the bridge are hollow cast iron caissons, 2 inches thick and sunk to bedrock. The bridge itself is not original, but the caissons date back to 1854. Does anyone know of any older bridge components still in use?
Carrollton Viaduct on the B&O, completed in 1829?
Here’s a link to several stone arch viaducts in Maryland that are older than any steel bridges.
This information was found by performing a simple Google search using the term “stone arch viaducts” and there were several other hits.