Henry Flagler started building his Overseas Railroad from Miami to Key West in the early 1900s. For many, it was considered a pipe dream but on Jan 22, 1912 he was on the first train into Key West. The completion of the railroad changed everything. Flagler died on May 20, 1913 but his railroad flourished until much of was destroyed by the Labor Day hurricane in 1935 with sustained winds of 185 mph and a 17-foot storm surge. Over the years leading up to WWII, much of the railroad right-of-way became what is now the Overseas Highway. Many of the old bridges, decommissioned and replaced by modern ones due to time and a salty environment, were given new life as fishing piers.
The New Seven Mile Bridge was opened in 1982. The old bridge is now listed on the National Register and has become a favorite of locals for walking, running and biking.
Update 4-Jul-2016: The bridge is now closed for about four years for major renovations.