The favorite bridge near me is th Eads Bridge, financed by Andrew Carnegie. It opened in 1874 and is still in use today. It was the first all steel bridge, the first to exclusively use cantilever supports, and still has some of the deepest caissons ever sunk. Fifteen people died from "the bends" during its construction.
To prove that the structure was safe they walked an elephant across it, because as everyone knew at the time, an elephant would not walk onto an unsafe structure. Science at its best!
https://en.wikipedia.org/wiki/Eads_Bridge