The victors of South Mountain slept upon the field of battle, on the night of September 14th. On the morning of the 15th, at early dawn, the Union pickets were pressed forward, and it was found that the dejected rebels had retired under cover of the night. An immediate pursuit was ordered. The army moved forward at once, in three columns. The first, containing the main force of cavalry, and led by Generals Pleasanton, Sumner, Hooker and Mansfield, advanced along the national turnpike road, by way of Boonsboro’. The second, led by Generals Burnside and Porter, moved by the old Sharpsburgh road. The third, led by General Franklin, went by Pleasant Valley, to occupy Robersville, and relieve Harper’s Ferry. The latter had not gone far, however, when the cessation of firing in the direction of the Ferry, gave notice that Colonel Miles had yielded his post. Still, in all directions, the advance pressed onward. It soon became evident that the rebels were taking up a strong position in front, and that a general battle was impending. General McClellan immediately went forward, examined the ground, to direct the formation of the Union line of battle. The rebels had fortified themselves on the west bank of Antietam creek, where they displayed their infantry, cavalry and artillery, in large force. The Union corps were massed on and near the Sharpsburgh road. During the 15th and 16th, both armies manœuvred for advantages of position; but the general battle—one of the most important that was fought during the war—did not commence until daybreak of the 17th. At this time, the relative positions of the combatants were as follows: Hooker, with his corps, consisting of General Rickett’s, Meade’s and Doubleday’s divisions, had crossed Antietam creek on the afternoon of the previous day; and, after some sharp skirmishing with the enemy, had gained the desired position, and bivouacked for the night. General Mansfield’s corps consisting of the divisions of William and Green, had crossed the creek during the night, and taken up position, a mile in rear of General Hooker. On the right of the turnpike, near the creek, was posted a division of General Sumner’s corps, under command of General Richardson; and, on the left, in line with Richardson, a division of General Porter’s corps, under command of General Sykes. The batteries of Captain Taft, Langrel, Von Kleiner, and of Lieutenant Weaver, each of twenty-pounder Parrott guns, were placed in front of the Sharpsburgh turnpike. Captain Weed’s three-inch, and Lieutenant Benjamin’s twenty-pounder batteries were on the crest of the hill, in the rear and right of bridge number three that crossed the creek; and the division of General Couch with General Franklin’s corps, in front of Brownsville, in Pleasant Valley,—with a large force of the enemy directly in front. The position of the enemy was a very favorable one. It is thus described by General McClellan: