Fortifications

Fort Slemmer sometimes called Battery Slemmer was one of seven temporary earthwork forts part of the Civil War Defenses of Washington, D.C., during the Civil War built in the Northeast quadrant of the city at the beginning of the Civil War by the Union Army to protect the city from the Confederate Army. From west to east, the forts were as follow: Fort Slocum, Fort Totten, Fort Slemmer, Fort Bunker Hill, Fort Saratoga, Fort Thayer and Fort Lincoln.  

The  fort was named in honor of Lieutenant Adam J. Slemmer. It was built in August 1861 between Fort Totten and Fort Bunker Hill on the east side of Harewood Road just north of The Catholic University of America's Marist Hall.[1] In February 1862, the 20th New York moved in the fort.  ( Source - Wikipedia )