...wo divisions, he marched day and night, recrossing the Potomac and reaching Sharpsburg on the 16th, followed by Walker. For the purpose of facilitating this reunion, Lee had retraced his steps from Frederick , directing the only two divisions Longstreet had left under Hood and Jones to move to Hagerstown, west of the mountains, while D. H. Hill with his division should halt at Boonsboroa, where were parke...