known to him at the time, that my left, from the time I left Washington, always rested on the Potomac, and my center was continually in position to re-enforce the left or right, as occasion might require. Had I advanced my left flank along the Potomac more rapidly than the other columns marched upon the roads to the right, I should have thrown that flank out of supporting distance of the other troops and greatly exposed it, and if I had marched the entire army in one column along the bank of the river, instead of upon five different parallel roads, the column, with its trains, would have extended about 50 miles, and the enemy might have defeated the advance before the rear could have reached the scene of action. Moreover, such a movement would have uncovered the communications with Baltimore and Washington on our right and exposed our right and rear. I presume it will be admitted by every military man that it was necessary to move the army in such order that it could at any time be concentrated for battle; and I am of opinion that this object could not have been accomplished in any other way than the one employed. Any other disposition of our forces would have subjected them to defeat in detached fragments.
On the 10th of September I received from my scouts information which rendered it quite probable that General Lee's army was in the vicinity of Frederick, but whether his intention was to move toward Baltimore or Pennsylvania was not then known. On the 11th I ordered General Burnside to push a strong reconnaissance across the National road and the Baltimore and Ohio Railroad toward New Market, and, if he learned that the enemy had moved toward Hagerstown, to press on rapidly to Frederick, keeping his troops constantly ready to meet the enemy in force. A corresponding movement of all the troops in the center and on the left was ordered in the direction of Urbana and Poolesville.
On the 12th a portion of the right wing entered Frederick, after a brisk skirmish at the outskirts of the city and in the streets.
On the 13th the main bodies of the right wing and center passed through Frederick. It was soon ascertained that the main body of the enemy's forces had marched out of the city on the two previous days, taking the roads to Boonsborough and Harper's Ferry, thereby rendering it necessary to force the passes through the Catoctin and South Mountain ridges and gain possession of Boonsborough and Rohrersville before any relief could be extended to Colonel Miles at Harper's Ferry.
On the 13th an order fell into my hands, issued by General Lee, which fully disclosed his plans, and I immediately gave orders for a rapid and vigorous forward movement. The following is a copy of the order referred to:
HEADQUARTERS ARMY OF NORTHERN VIRGINIA,
September 9, 1862.
The army will resume its march to-morrow taking the Hagerstown road. General Jackson's command will form the advance, and, after passing Middletown, with such portion as he may select, take the route toward Sharpsburg, cross the Potomac at the most convenient point, and, by Friday night, take possession of the Baltimore and Ohio Railroad, capture such of the enemy as may be at Martinsburg, and intercept such as may attempt to escape from Harper's Ferry.
General Longstreet's command will pursue the same road as far as Boonsborough, where it will halt with the reserve, supply, and baggage trains of the army.
General McLaws, with his own division and that of General R. H. Anderson, will follow general Longstreet. On reaching Middletown he will take the route to Harper's Ferry, and by Friday morning possess himself of the Maryland Heights, and endeavor to capture the enemy ;at Harper's Ferry and vicinity.
General Walker, with his division, after accomplishing the object in which he is