Black workers pose with tools and spikes as they rebuild a railroad line in northern Virginia. These men were employed by the United States Military Railroad (USMR), an agency created by the U.S. War Department during the Civil War to maintain, build, and rebuild track and railroad bridges. Many enslaved men who escaped to freedom behind Union lines gathered at railroad junctions and worked for the agency. They worked in the extensive rail yards in Alexandria; they served on construction crews as laborers; and some became train brakemen and firemen. The success of the USMR was a key element in the federal victory, as trains were critical in transporting soldiers and supplies.