...1th, with 15,562 present for duty, under Sigel; and the 12th, with 12,162, under Slocum, which Burnside called his reserve grand division. These troops, under command of Sigel, were on the march to Fredericksburg , but they did not arrive until after the battle. Besides these, there were 51,970 holding the line of the Potomac above Washington, and the fortified lines about the city and Alexandria, with 284...