Fort Carroll Fort Carroll is a artificial island and abandoned fort in the middle of the Patapsco River , just south of Baltimore , Maryland . It is named for Charles Carroll of Carrollton ( 1737 - 1832 ) , a signer of the Declaration of Independence . Design and construction . In 1847 , the State of Maryland gave permission to the United States War Department to construct a fort in the shallow water of Soller ’ s Point Flats to protect the city of Baltimore . Fort Carroll was important for the defense of Baltimore — before the fort was created , Fort McHenry , just outside the city , was the only military defensive structure between Baltimore and the Chesapeake Bay . The fort was part of the " Permanent System " or Third System construction program , which aimed to defend America ’ s most important ports . Then Brevet - Colonel Robert E . Lee designed the hexagonal structure and supervised the construction , which the U . S . Army Corps of Engineers commenced in 1848 . Lee went on to become Superintendent of the United States Military Academy at West Point before the fort was named on 8 October 1850 . In addition , in 1853 a lighthouse , now abandoned , was built on the ramparts to aid navigation into Baltimore Harbor . In 1898 a new lighthouse was built , the one still seen today . It was automated in 1920 and discontinued operations before 1945 . The original design foresaw the fort being armed with some 225 cannon on three levels . However , in April 1861 at the outbreak of the Civil War , Fort Carroll ' s walls were still less than half the planned height of thirty feet . Only five gun platforms were ready and only two were armed with guns . Still , the Army emplaced about thirty cannon and manned the fort throughout the war . In April 1864 torrential rains flooded the fort ’ s magazines , which led the Army to move all the powder and ammunition to Fort McHenry . Spanish - American War . When the United States entered into the Spanish - American War in 1898 , the Army again manned the fort ' s batteries , which were by then completely obsolete . The Army therefore commenced the construction of modern concrete gun emplacements following the designs of the Endicott Board . The Army created three batteries : Battery Towson ( two 12 " barbette disappearing carriage guns ) , Battery Heart ( two 5 " balanced pedestal - mount guns ) and Battery Augustin ( two 3 " balanced pedestal - mount guns ) . The new batteries were ready by September 1900 , well after the end of the war . They received their names on 30 March 1903 . World War I and abandonment . After World War I broke out , in 1917 the Army removed the guns from Battery Heart and in 1918 those from Battery Towson to use elsewhere . By 1920 , all guns had been removed from the fort . In March 1921 the Army officially abandoned Fort Carroll and moved whatever military equipment was left to nearby Fort Howard . The War Department declared the island excess property in 1923 , but took no immediate steps to sell the land . A variety of proposals for the use of the island were advanced , including a prison , as well as a 1923 plan advanced by Baltimore mayor William Broening to place an electric " Welcome to Baltimore " sign on the island , accompanied by a statue of Lord Baltimore . In World War II the Army used the fort as a firing range . It also served as a checkpoint for vessels . In May 1958 , Baltimore attorney Benjamin Eisenberg purchased the island for $ 10 , 000 , intending to put a casino on the island , but development plans never materialized . The fort is now deserted and the habitat for various animals . It is also a site for occasional urban explorations .