Fort Jackson was an American Civil War-era fortification in Virginia that defended the southern end of the Long Bridge, near Washington, D.C. Long Bridge connected Washington, D.C. to Northern Virginia and served as a vital transportation artery for the Union Army during the war. Fort Jackson was named for Jackson City, a seedy suburb of Washington that had been established on the south side of the Long Bridge in 1835. It was built in the days immediately following the Union Army's occupation of Northern Virginia in May 1861. The fort was initially armed with four cannon used to protect the bridge, but these were removed after the completion of the Arlington Line, a line of defenses built to the south. After 1862, the fort lacked weapons except for small arms and consisted of a wooden palisade backed by earthworks. Two cannon were restored to the fort in 1864 following the Battle of Fort Stevens. The garrison consisted of a single company of Union soldiers who inspected traffic crossing the bridge and guarded it from potential saboteurs.
Following the final surrender of the Confederate States of America in 1865, Fort Jackson was abandoned. The lumber used in its construction was promptly salvaged for firewood and construction materials and, due to its proximity to the Long Bridge, the earthworks were flattened in order to provide easier access to Long Bridge. In the early 20th century, the fort's site was used for the footings and approaches to several bridges connecting Virginia and Washington. Today, no trace of the fort remains, though the site of the fort is contained within Arlington County's Long Bridge Park, and a National Park Service 2004 survey of the site indicated some archaeological remnants may still remain beneath the park.(Wikipedia)