In the fall of 1861, after their July defeat at Manassas (Bull Run), Union forces retreated to Washington, D.C. to organize and retrain, while Confederate forces concentrated in Centreville to strengthen the defense of Northern Virginia and protect access to the Orange and Alexandria Railroad leading to Richmond, the Southern Capital. As winter set in, 40,000 men built a 5-mile defensive line along Centreville’s high ground from Cub Run on the west, around Centreville, to Little Rocky Run on the south. Using local lumber, they built log huts for winter quarters, and Confederate General Johnston established headquarters at Mount Gilead, an early 18th century house across Mount Gilead Road west of the site. The surviving earthen mound was part of a defensive network of earthworks and fortifications that included thirteen battery positions for seventy-one field guns. When Union forces later marched to Centreville, they discovered that the defenses had partly deceived them because the fortifications were supported by Quaker Guns, logs painted black to look like cannon. Later in the war, Union forces reused the earthworks and forts and extended them to fully encircle Centreville.