They definitely require routine maintenance and inspection.
The Nondestructive Testing article I linked to in another comment said "significant environmental damage requiring repair typically occurs before the average bridge reaches mid-life."
It would be very interesting to know how bridge metrics (length, load specification, etc.) relate the longevity. Of course, some bridges last for centuries, but some last for decades. This is an order of magnitude!
Spoiler: they don't, yet they do, Theseus' ship-style. For all the centuries-old bridges still in use around here, there's only a few bits and pieces left from the original, the rest has been replaced multiple times over as a part of maintenance.
The difference here is probably maintainability: for a stone arch design, you can prop it up for safety, replace a few stones, and voila, like new. For a cable-stayed and/or concrete design...not really. In other words, the bridges that have "lasted for centuries" have hot-swappable parts ;)
