The Situation on 10 September: Before dawn on the 10th most of the Army of Northern Virginia, Gen Jackson in the lead, leave their camps around Frederick heading northwest along the National Road. They form detachments called for in Gen Lee's Special Orders 191 with the mission to clear the Federal garrisons at Martinsburg and Harpers Ferry, Virginia. Jackson's Command reaches near Boonsboro, Longstreet's (with Lee -the "main body") to just beyond Middletown, and McLaws' Division to near Burkittsville. Walker's Division, on the march since about 9:00 pm of the 9th, was on a mission to destroy the Moncacy Aqueduct, but gets new orders in 191 and backtracks to cross the Potomac into Virginia near Point of Rocks at days end.
Hill's Division remains just south of Frederick as the rear guard, screened by Stuart's Cavalry along the Monocacy.
Meantime, Gen McClellan continues to push his infantry forward seeking the ANV. His left under Franklin to near Poolesville, and his center, under Sumner, to Clarksburg (XII Corps) and Damascus (II Corps).