I see Steve posted an old railroad pic, here is one from "my backyard" of the B&O Royal Blue traversing the Thomas Viaduct in 1937. This bridge crosses the Potapsco River valley near Elkridge, MD (not far from my home) and was the first stone/mason bridge of its type built in America on a curve...it was finished in 1835 and for its time was considered an engineering marvel. It is still in constant use today.
Read more about the bridge here:
http://en.wikipedia.org/wiki/Thomas_Viaduct