When I was in high school (circa 1990), an extraordinary number of bridges in Vermont were crumbling, all at the same time.  This is because they were all built in 1928 – 1929, and 60 years was apparently the lifespan of those materials given the upkeep and conditions.  The reason all the bridges were built in such a short window of time was the great flood of 1927, which washed away over 1200 bridges in the state.

The Vermont Historical Society has this incredible video on the event, which is really something to behold (embedded below).