Fortifications

Fort Bennett (1861-1865) - A Union U.S. Civil War Fort first established in 1861 in present day Arlington County, Virginia. Named Fort Bennett in G.O. 18, 30 Sep 1861, after Captain Michael P. Bennett, 28th New York Infantry, who  supervised construction of the fort.  Abandoned in 1865 at the end of the war. 

Fort Bennett was one of 33 forts on the Virginia side of the Potomac River that made up an outer defense line for Washington DC known as the Arlington Line.   ( Source - Wikipedia )