It shall be the duties of the commissioners, under the direction of the Secretary of the Interior, to superintend the opening or repair of such roads as may be necessary to the purposes of the battlefield, and to ascertain and mark with historical tablets or otherwise, as the Secretary of the Interior may determine, all breastworks, earthworks, walls, or other defenses or shelters, lines of battle, location of troops, buildings, and other historical points of interest within the battlefield or in its vicinity, and the said commission in establishing the battlefield shall have authority, under the direction of the Secretary of the Interior, to employ such labor and service at rates to be fixed by the Secretary of the Interior, and to obtain such supplies and materials as may be necessary to carry out the provisions of sections 423, 423a, and 423b to 423h of this title.