Fort Mulligan was constructed from August through December of 1863 by Union troops under Colonel James A. Mulligan of Chicago, Illinois, with infantry, cavalry, and artillery from West Virginia, Pennsylvania, Maryland, and Illinois performing the labor. Known locally as Fort Hill, it was intended to protect the South Branch Valley from Confederate forces and to serve as an auxiliary depot supplying numerous Union expeditions. Built on ground that had previously held fortified camps in October 1861 and in May and June 1862, the fort consisted of dirt earthworks with timber-lined inner walls, outer entrenchments protected by an abatis of cut trees, as many as three entrances, at least seven gun emplacements, and four bombproofs for rifle and artillery ammunition. The South Branch of the Potomac River valley saw heavy troop activity throughout the Civil War, and this hill and its surrounding area were occupied by Federal or Confederate forces as early as August 1861 and during at least part of every year of the war. Federal forces repeatedly used this strategic point to hinder raids on the B&O Railroad to the north and as a jumping-off point for raids farther south, while foraging wagon trains and many Union expeditions were supplied from the depot at Petersburg, often reinforced by soldiers from Fort Mulligan. The fort was evacuated on January 31, 1864, by Union Colonel Joseph Thoburn because of an impending attack by Confederate General Jubal Early, whose men, he said, demolished the works. Sharp fighting continued sporadically in the area through the rest of 1864 and 1865, but Fort Mulligan was never again occupied as a garrison. The site also preserves the story of Joshua Winters, a private in Company G, First Western Virginia Volunteer Infantry, whose diary and weekly letters to his sisters provide glimpses of life for a typical Union soldier at the fort.
