Fortifications

The fort, built on an isolated hill belonging to Dr. William Manning, guarded the approaches to Washington City from southern Maryland to Benning's Bridge which crossed the Anacostia River. Some earthworks remain on 42nd St. N.E.

Colonel John G. Barnard, supervising engineer of the Defenses of Washington, contended that the fort was “a powerful influence in preventing an enemy, coming from the direction of Bladensburg, from reaching the margins of the Anacostia opposite Washington.” The fort was named for legendary West Point Professor Dennis Hart Mahan who taught many of the military officers that served in Union and Confederate armies during the Civil War. It was completed and ready for a garrison in December 1861. Nevertheless, the fort and its armament underwent extensive modification throughout the war.

Fort Mahan was one of the last forts to be abandoned at the end of the war, being one of 11 works that occupied commanding positions around Washington. However, it later reverted back to the Manning family. Today, Fort Mahan is a recreational park.