On Saturday, the 13th, Lee determined to draw back Longstreet from his advanced position, in view of the fact that Jackson had not yet reduced Harper's Ferry and that McClellan was marching to its relief. Longstreet's divisions therefore approached Boonsboro so as to support D. H. Hill, and thus it happened that they took part in the battle of South Mountain. Hill again occupied the summit where we found him on the 14th. From all this it is very plain that if McClellan had hastened his advance on the 13th, the passes of South Mountain at Turner's and Fox's gaps would not have been occupied in force by the enemy, and the condition of things would have been what he believed it was on the morning of the 14th, when a single brigade had been thought enough to support Pleasonton's reconnoissance. Twenty-four hours had changed all that.
The turnpike from Boonsboro to Sharpsburg continues southward a couple of miles, crossing the Potomac to Shepherdstown, which lies on the Virginia side of the river. A bridge which formerly carried the road over the stream had been burned; but not far below the ruined piers was a ford, which was a pretty good one in the present stage of water. Shepherdstown was the natural place of junction for Lee and Jackson; but for Lee to have marched there at once would have exposed Jackson to attack from the northern side of the Potomac. The precious stores and supplies captured at Harper's Ferry must be got to a place of safety, and this was likely to delay Jackson a day or two. Lee therefore ordered McLaws to obstruct Franklin's movement as much as he could, whilst he himself concentrated the rest of Longstreet's corps at Sharpsburg, behind the Antietam. If McClellan's force should prove overwhelming, the past experience of the Confederate general encouraged him to believe that our advance would not be so enterprising that he could not make a safe retreat into Virginia. He resolved therefore to halt at Sharpsburg, which offered an excellent field for a defensive battle, leaving himself free to resume his aggressive campaign or to retreat into Virginia according to the result.
McClellan had ordered Richardson's division of the Second Corps to support the cavalry in the advance, and Hooker's corps followed Richardson. [Footnote: Hooker's Report, Official Records, vol. xix. pt. i. p. 216.] It would seem most natural that the whole of Sumner's wing should take the advance on the 15th, though the breaking up of organizations was so much a habit with McClellan that perhaps it should not be surprising that one of Sumner's divisions was thus separated from the rest, and that Burnside's right wing was also divided. [Footnote: We must not forget the fact, however, that the order dividing the army into wings was suspended on that morning, and that this gives to the incident the air of an intentional reduction of the wing commanders to the control of a single corps. Official Records, vol. xix. pt. ii. p. 297.] The Ninth Corps was ordered to follow the old Sharpsburg road through Fox's Gap, our line of march being thus parallel to the others till we should reach the road from Boonsboro to Sharpsburg.
But we were not put in motion early in the day. We were ordered first to bury the dead, and to send the wounded and prisoners to Middletown It was nearly noon when we got orders to march, and when the head of column filed into the road, the way was blocked by Porter's corps, which was moving to the front by the same road. As soon as the way was clear, we followed, leaving a small detachment to complete the other tasks which had been assigned us. In the wooded slope of the mountain west of the gap, a good many of the Confederate dead still lay where they had fallen in the fierce combats for the possession of the crest near Wise's house. Our road led through a little hamlet called Springvale, and thence to another, Porterstown, near the left bank of the Antietam, where it runs into the Boonsboro and Sharpsburg turnpike. Sumner's two corps had taken temporary position on either side of the turnpike, behind the line of hills which there borders the stream. Porter's corps was massed in rear of Sumner, and Hooker's had been moved off to the right, around Keedysville. I was with the Kanawha division, assuming that my temporary command of the corps ended with the battle on the mountain. As we came up in rear of the troops already assembled, we received orders to turn off the road to the left, and halted our battalions closed in mass. It was now about three o'clock in the afternoon. McClellan, as it seemed, had just reached the field, and was surrounded by a group of his principal officers, most of whom I had never seen before. I rode up with General Burnside, dismounted, and was very cordially greeted by General McClellan. He and Burnside were evidently on terms of most intimate friendship and familiarity. He introduced me to the officers I had not known before, referring pleasantly to my service with him in Ohio and West Virginia, putting me upon an easy footing with them in a very agreeable and genial way.
We walked up the slope of the ridge before us, and looking westward from its crest, the whole field of the coming battle was before us. Immediately in front the Antietam wound through the hollow, the hills rising gently on both sides. In the background, on our left, was the village of Sharpsburg, with fields enclosed by stone fences in front of it. At its right was a bit of wood (since known as the West Wood), with the little Dunker Church standing out white and sharp against it. Farther to the right and left, the scene was closed in by wooded ridges with open farm lands between, the whole making as pleasing and prosperous a landscape as can easily be imagined.
We made a large group as we stood upon the hill, and it was not long before we attracted the enemy's attention. A puff of white smoke from a knoll on the right of the Sharpsburg road was followed by the screaming of a shell over our heads. McClellan directed that all but one or two should retire behind the ridge, while he continued the reconnoissance, walking slowly to the right. I think Fitz-John Porter was the only general officer who was retained as a companion in this walk. I noted with satisfaction the cool and business-like air with which McClellan made his examination under fire. The Confederate artillery was answered by a battery of ours, and a lively cannonade ensued on both sides, though without any noticeable effect. The enemy's position was revealed, and he was evidently in force on both sides of the turnpike in front of Sharpsburg, covered by the undulations of the rolling ground which hid his infantry from our sight.
The examination of the enemy's position and the discussion of it continued till near the close of the day. Orders were then given for the Ninth Corps to move to the left, keeping off the road, which was occupied by other troops. We moved through fields and farm lands, an hour's march in the dusk of evening, going into bivouac about a mile south of the Sharpsburg bridge, and in rear of the hills bordering the Antietam.
The village of Sharpsburg is in the midst of a plateau which is almost enclosed by the Potomac River and the Antietam. The Potomac bounds it on the south and west, and the Antietam on the east. The plateau in general outline may be considered a parallelogram, four miles in length from north to south, and two and a half miles in width inside the bends of the river. The northern side of this terrain appears the narrowest, for here the river curves sharply away to the west, nearly doubling the width of the field above and below the bend. From the village the ground descends in all directions, though a continuous ridge runs northward, on which is the Hagerstown turnpike. The Boonsboro turnpike enters the village from the northeast, crossing the Antietam on a stone bridge, and continuing through Sharpsburg to the southwest, reaches Shepherdstown by the ford of the Potomac already mentioned. The Hagerstown turnpike enters the town from the north, passing the Dunker Church a mile out, and goes nearly due south, crossing the Antietam at its mouth, and continuing down the Potomac toward Harper's Ferry.
The Antietam is a deep creek, with few fords at an ordinary stage of water, and the principal roads cross it upon stone bridges. Of these there were three within the field of battle; the upper one in front of Keedysville, the middle one upon the Boonsboro turnpike, and the lower one on the Sharpsburg and Rohrersville road, since known as Burnside's bridge. McClellan's staff was better supplied with officers of engineers than the staff of most of our separate armies, and Captain Duane, his chief engineer, systematized the work of gathering topographical information. This was communicated to the general officers in connection with the orders which were given them. In this way we were instructed that the only fords of the Antietam passable at that time were one between the two upper bridges named, and another about half a mile below Burnside's bridge, in a deep bend of the stream. We found, however, during the engagement of the 17th, another practicable crossing for infantry a short distance above the bridge. This was not a ford in common use, but in the low stage of water at the time it was made available for a small force.