Battle Of Antietam, fought by the national army of the Potomac, under Gen. George B. McClellan, and the confederate army of North Virginia, under Gen. Robert E. Lee, between Sharpsburg and the Antietam creek, an affluent of the Potomac river, Sept. 10 and 17, 1862. After the defeat of the army of the Potomac in the seven days' fighting on the line of the Chickahominy, the confederates prepared for an invasion of Maryland, worsted Pope's army at Cedar Mountain, in the second battle of Bull Run, and at Chantilly, crossed the Potomac near Leesburg, and concentrated their forces at Frederick. Meanwhile the national army had been withdrawn from Harrison's Landing and consolidated at Washington with Pope's command, and the whole, under McClellan, moved out to meet Lee. The right wing, consisting of the 1st and 9th corps, was under Burnside; the centre, composed of the 2d and 12th corps, was under Sumner; and the left wing, composed of the 6th corps, was under Franklin. In this order McClellan marched by the Rockville turnpike, the right wing of his army extending toward the Baltimore and Ohio railroad, and the left toward the Potomac. His advanced guard entered Frederick as the confederate rear guard was leaving it.

At this place, on Sept. 12, he became acquainted with the disposition of Lee's forces, as well as with his immediate plans, through a copy of Lee's marching orders which one of the confederate commanders had inadvertently left behind him. Lee, having captured all the outlying detachments of the national army, including that in the stronghold of Harper's Ferry, and thus secured his communication with Richmond, concentrated all his available forces, choosing his position in front of Sharps-burg, in the angle between the Potomac, which covered his rear, and the Antietam, whose deep bed and precipitous sides covered his front. Lee's line, forming almost a semicircle about the village, covered all the roads concentrating at that place; its right wing rested on the heights dominating the creek, and stretched along it, sweeping all the crossings for more than half a mile; the centre occupied the open fields and patches of wood extending to the Hagerstown road, and the left rested upon the Potomac. McClellan's army approached the battlefield along the turnpike leading from Keedysville to Sharpsburg, his main body going into position on the left bank of the Antietam on the afternoon of Sept. 15. No fighting took place on this day.

The greater part of the 16th was passed in harmless cannonading, but late in the afternoon McClel-lan threw forward Hooker's corps, with orders to force a passage of the Antietam by the upper one of the four stone bridges spanning the creek in that neighborhood. This bridge, being beyond the reach of the confederate line, had been left undefended, and Hooker's crossing was therefore quickly and easily made. Pushing forward at once through a narrow piece of woods, he soon struck the confederate left under Hood, and after a sharp skirmish, terminating with nightfall, in his favor, his corps rested on their arms near the Hagers-town road, almost in contact with the enemy's line. This advance served to place one corps of 18,000 men in a good position to give battle as well as to uncover the other crossings of the Antietam as far down as the Keedysville road, thus rendering it easy for McClellan to secure his initiatory movement, by sending Mansfield's 12th corps, under cover of darkness, to strengthen Hooker. On the morning of the 17th the disposition of the combatants was as follows: Lee's position was substantially unchanged; his entire army, estimated at about 65,000 strong, was formed in a semicircular line covering the roads converging at Sharpsburg. Hooker's and Mansfield's corps of McClellan's army had crossed the Antietam and held advanced positions on the extreme right; Sumner's corps held itself in readiness to cross; Porter's corps was in reserve, covering the Keedysville bridge, but separated from the enemy by the creek; and Burnside's corps occupied the extreme left, and was also separated from the confederate position by the Antietam. The aggregate strength of these corps was about 85,000 men; but being partly on one side and partly on the other side of a stream which could hardly be crossed anywhere except by a bridge, and which was particularly easy to defend, the superior strength of the Union army counted but for little in the bloody conflict which followed.

McClellan's plan was for Hooker and Mansfield, supported by Sumner, to attack the confederate line, and engage it so closely as to permit Burnside, advancing simultaneously, to force a passage at the lower bridge, and thus unite all the corps except the reserve on the further side of the Antietam, with their entire strength available for the final struggle. Hooker's corps held a position close to the enemy's line, and was therefore forced to begin skirmishing almost as soon as it was light. After gaining some slight advantages it attacked with great fury, and succeeded in forcing Lee's left under Jackson backward for nearly half a mile before it received the slightest check. Hooker gave his men a short breathing spell, and dashed forward again; but his divisions were already fatigued as well as greatly shattered by their bloody work. Meeting the reserves of the enemy's left, they were in turn driven back to the position from which they advanced less than an hour before, notwithstanding Mansfield had in the mean time hastened forward to join in the conflict.

This gallant veteran lost his life in trying to regain the ground lost by Hooker, and, although aided by a terrible fire from the reserve artillery of the Union army, stationed near the Keedysville bridge, his corps was also forced to retire to the position from which it had advanced. McClellan now ordered Sumner to advance, and this resolute commander accordingly made his appearance on the battlefield about 9 o'clock, and with all the precision of a parade moved his corps of four divisions against the confederate line, over a part of the field somewhat to the left of that covered by Hooker and Mansfield, but directed mainly against the woods to the west of the Dunker church on the Hagerstown road. The confederates, having had time to rectify and strengthen their lines, received this formidable attack with steadiness; but so fierce was the onset of Sumner's right division under Sedgwick, that the confederate division confronting him was driven back into and beyond the woods, when it was strongly reenforced by troops which had arrived upon the field only that morning. The confederates now made a spirited counter attack, directing their movement mainly against Sedgwick, who was in echelon with the other divisions of Sumner's corps, and therefore poorly supported by them.

The fighting which ensued was characterized by the greatest bravery, but when it ceased Sumner's entire corps was also defeated, and the enemy's line completely restored. By 11 o'clock half of the Union army and nearly all of the confederate army had been engaged. The latter, standing in a close and compact line, on its own chosen ground, had been able to act as a unit, while the former at the out-start was divided by the Antietam, and had spent its force in gallant but disconnected attacks, resulting in defeat by detail, accompanied by an immense loss of life. Had Lee known at any time during the afternoon the extent of the injury he had inflicted upon the right wing of the Union army, and assumed the offensive, it is scarcely to be doubted that he would have gained a complete victory notwithstanding the timely arrival of Franklin's corps on that part of the field. Neither Burn-side's nor Porter's corps had yet been seriously engaged, although the former had been ordered to attack simultaneously with the other corps. His failure to carry the bridge in his front and to effect a lodgment beyond was due to the fact that it was swept by the sharpshooters of the enemy's right, occupying the commanding hillocks close to the borders of the creek.

The confederate position here was very strong, and, being covered by the Antietam, almost entirely impassable in this portion of its course, was practically unassailable. Burnside advanced promptly as ordered, but his foremost troops encountered such a galling fire that they could not even reach the bridge, much less carry it. After several hours' delay Burnside succeeded in throwing one brigade across the creek by a ford which had been discovered some distance below, thus relieving the pressure in his front, and permitting the main body of his corps to cross by the bridge and to secure a good position on the right bank of the creek. After reforming his lines Burnside advanced, carried the heights beyond, and pressed back the enemy's right several hundred yards; but his attack not being supported by detachments from the other parts of the army, as it should have been, he was defeated and driven back almost to the creek, as the other corps had been. Night ended the conflict with both armies concentrated and confronting each other on the W. side of the Antietam. On the 18th McClellan stood on the defensive.

During the day he received the re-enforcement of two strong divisions under Humphreys and Couch, and then resolved to attack the next day; but meantime Lee had made good his retreat to the south side of the Potomac. McClellan's loss in this action was 2,010 killed, 9,416 wounded, and 1,043 missing; total, 12,469. Lee's army, having fought on the defensive throughout, and frequently under cover, is estimated by confederate writers to have lost only about 9,000. This battle was followed rather by negative than positive military results. The confederate army retired to Virginia and assumed a defensive attitude; the people of Maryland did not rise in rebellion, and the national capital did not fall into the hands of the invaders. On the other hand, the political measure which followed it was positive and far-reaching in its effects. President Lincoln had made a solemn vow that if Gen. Lee was driven back from Maryland, he would crown the result by issuing a proclamation abolishing slavery, which was done, at least conditionally, on the 22d day of September, 1802.