Constructed between 1846-1875, Fort Jefferson ranks as one of the largest coastal forts ever built, covering an area of nearly 17 acres. Located within the remote group of islands known as the Dry Tortugas, the fort's isolated position at the extreme western tip of the Florida Keys complicated construction efforts. Yet it was the fort's location, guarding the entrance to the Gulf of Mexico and overlooking one of the world's busiest shipping lanes, that underscored its strategic importance. Enslaved African Americans were instrumental in the construction of Fort Jefferson. Hired primarily from their owners in Key West, enslaved laborers endured isolation, harsh conditions, and deadly outbreaks of disease to build the island fortress. Due to its remote location there was perhaps no area in America that presented a greater challenge to self-emancipation. Nevertheless, seven men attempted to escape from the fort in 1847. By 1863, the fort's slave rolls were discontinued. Exemplifying the sweeping changes brought about by the Civil War, African Americans returned to Fort Jefferson in 1865, but as soldiers. No longer denied their freedom, African Americans were now guardians of freedom.