Still, the importance of moving with extreme caution was kept constantly in view, and the army was moved so that it extended from the railroad to the Potomac River, the extreme left flank resting on that stream.
On the twelfth of September, a portion of the right wing of the army entered Frederick, Md., and on the following day the main body of the right and the center wings arrived, only to find that the enemy had marched out of the place two days before, taking the roads to Boonesboro' and Harper's Ferry.
Lee had left a force to dispute the possession of the passes, through which the roads across South Mountain ran, while he had dispatched Jackson to effect the capture of Harper's Ferry. In these plans he was partially frustrated, for, while Jackson succeeded in capturing Harper's Ferry, McClellan drove the rebel troops from the passes, after short but vigorous engagements at South Mountain, on September 14th, but failed in his efforts to relieve Harper's Ferry, and that place was surrendered on the following day.
Immediately following the actions at South Mountain, Lee, being closely pressed by McClellan, turned at bay in the beautiful valley of the Antietam. Here he resolved to endeavor to hold his position until he could concentrate his army. His forces at this time numbered about forty thousand men.
On the sixteenth, he was reinforced by Jackson's gallant corps, numbering about five thousand men, which, together with other reinforcements, received during the day, swelled his numbers to fifty thousand men, which, in the language of one of their own writers, constituted "the very flower of the Army of Northern Virginia."
Our own forces did not exceed eighty-five thousand men, and it is but correct to say that not seventy thousand were actually engaged on the day of the great battle. My own judgment is, that at no time during the fight was the Confederate army ever confronted by a force outnumbering their own.
Confederate writers have sought to make it appear that Lee, at Antietam, fought and practically defeated a force in excess of his own in the ratio of three to one. This assertion is proven to be a glaring error, for the facts are that the odds were less than three to two, even in point of actual numerical strength present, while, all things considered, these were reduced until the two armies faced each other on the morning of Antietam pretty evenly opposed, and with no decided advantage in favor of either contestant.
To explain: taking it for granted that McClellan had eighty-seven thousand men at roll-call on the morning of the seventeenth, it is now known that the battle was mainly fought by the First, Second, Ninth and Twelfth Corps, while the Fifth and Sixth Corps and the Cavalry Division were scarcely used at all. In addition to this, it should be remembered that ours was the attacking force; that the enemy occupied a chosen position, and therefore, in this view of the situation, the odds were by no means great in favor of the Federal troops.
"My horse was shot under me while crossing the stream." P. 569