Fortifications

Fort Tillinghast was a small lunette that the Union Army constructed in Alexandria County (now Arlington County), Virginia, as part of the Civil War defenses of Washington.  Fort Tillinghast stood about 0.6 miles away from Arlington House, the Union-occupied estate of Confederate General Robert E. Lee. 

The lunette was named in honor of Captain Otis H. Tillinghast, Quartermaster, killed at the First Battle of Bull Run on July 21, 1861. Oriented to the west, it had a perimeter of 298 yards (272 m), emplacements for 12 guns, and two magazines as well as a bomb-proof. The fortification's armaments included four 24-pound guns, one 24-pound field howitzer, four 30-pound Parrott rifles, two 20-pound Parrott rifles, and two 24-pound Coehorn mortars.[1] Units garrisoned at the lunette included the 16th Maine Infantry, 1st Massachusetts Heavy Artillery, 4th New York Heavy Artillery, and the 145th and 138th Ohio Infantry.  ( Source - Wikipedia )