Florida Historical Markers Programs - Marker Detail

Description: Side One: Between 1905 and 1912, Henry Flagler extended his Florida East Coast (FEC) Railway to Key West. This massive engineering project, called the Overseas Railroad, required 23 bridges that utilized the most innovative technology of the time. The laborers who built the bridges came from around the United States and other countries. Whereas Flagler’s railway was mostly on land, the 6.7 miles between Knights Key and Little Duck Key were the longest over-water expanse. The bridge’s design utilized a variety of span types: steel girder deck spans, 9,000 feet of concrete arch viaduct, and a metal truss swing span. An important element of Flagler’s design was for the Old Seven Mile Bridge to cross over Pigeon Key, since the key was located between the two ends of the bridge. Pigeon Key was used as an FEC staging area during construction of the Overseas Railroad and later served as a permanent FEC camp. The bridge was historically known as the Flagler Viaduct but has also been referred to as the Knights Key Bridge, the Seven Mile Bridge, and more recently, the Old Seven Mile Bridge. The Overseas Railroad was severely damaged by the deadly 1935 Labor Day Hurricane and subsequently abandoned. Side Two: In 1936, the State of Florida purchased the abandoned Florida East Coast (FEC) Railway right-of-way for $640,000. Between 1936 and 1938, the rail bridges were converted to vehicular use. The conversion of the Overseas Railroad into the Overseas Highway required complex, specialized engineering for each bridge. The Old Seven Mile Bridge’s narrow foundations led engineers to place new metal I-beams across the bridge, upon which the new road was built. The FEC’s rails were re-used as guardrails and are still visible today. The completion of the Overseas Highway on March 29, 1938 allowed people to drive from Miami to Key West without having to take a ferry. The Old Seven Mile Bridge was recognized for its significant engineering and role in transportation in Florida when it was listed on the National Register of Historic Places in 1979. In 1982, a new bridge, located to the south, replaced the original one. In 2021, the Florida Department of Transportation completed the rehabilitation of approximately 2 miles of the Old Seven Mile Bridge to Pigeon Key, so that it would continue to serve as a testament to the engineering feats that were the Overseas Railroad and Highway.