[Illustration: (Cover) _Fort Jefferson from the air._] Fort Jefferson NATIONAL MONUMENT [Illustration: Lighthouse] _Fort Jefferson (1846-74), largest of the 19th-century American coastal forts, and one time “Key to the Gulf of Mexico.”_ The seven Dry Tortugas Islands and the surrounding shoals and waters in the Gulf of Mexico are included in Fort Jefferson National Monument. Though the area is off the beaten track, it has long been famous for bird and marine life, as well as for legends of pirates and sunken gold. The century-old fort is the central feature. _Dry Tortugas_ Like a strand of beads hanging from the tip of Florida, reef islands trail westward into the Gulf of Mexico. At the end, almost 70 miles west of Key West, is the cluster of coral keys called Dry Tortugas. In 1513, the Spanish discoverer Ponce de León named them _las Tortugas_—the Turtles—because of “the great amount of turtles which there do breed.” The later name Dry Tortugas, warns the mariner that there is no fresh water here. Past Tortugas sailed the treasure-laden ships of Spain, braving shipwreck and corsairs. Not until Florida became part of the United States in 1821 were the pirates finally driven out. Then, for additional insurance to a growing United States commerce in the Gulf, a lighthouse was built at Tortugas, on Garden Key, in 1825. Thirty-one years later the present 150-foot light was erected on Loggerhead Key. _The Need for a Fort_ In the words of the naval captain who surveyed the Keys in 1830, Tortugas could “control navigation of the Gulf.” Commerce from the growing Mississippi Valley sailed the Gulf to reach the Atlantic. Enemy seizure of Tortugas would cut off this vital traffic, and naval tactics from this strategic base could be effective against even a superior force. There were still keen memories of Jackson’s fight with the British at New Orleans, and Britain was currently developing her West Indies possessions. Trouble in Cuba was near. Texas, a new republic, seemed about to form an alliance with France or England, thus providing the Europeans with a foothold on the Gulf Coast. _Thirty Years of Construction_ During the first half of the 1800’s the United States began a chain of seacoast defenses from Maine to Texas. The largest link was Fort Jefferson, half a mile in perimeter and covering most of 16-acre Garden Key. From foundation to crown its 8-foot-thick walls stand 50 feet high. It has 3 gun tiers, designed for 450 guns, and a garrison of 1,500 men.