Fort Pickens was an important element in the defense of the U.S. The Third System fortifications consisted of 42 forts built between 1816 and 1870. They were used to guard all the principal harbors, rivers, and naval yards of the United States. Only the Advanced Redoubt of Fort Barrancas at Gulf Islands National Seashore was built entirely for land defense. There was no roadway system on the island or bridges to the mainland until the 20th Century. [Click here for park info](http://www.nps.gov/guis/parkmgmt/general-management-plan.htm)