William Swinton, Campaigns of the Army of the Potomac

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[326] in favor of his line of retreat, touching which he was justifiably nervous. Accordingly, instead of directing Longstreet and Hill to join Ewell on the intended invasion, he ordered them to march from Chambersburg, defiling through the South Mountain range, towards Gettysburg, distant twenty miles eastward; and he instructed Ewell to countermarch from York and Carlisle on the same point. These movements were begun on the morning of Monday, the 29th of June.

It was not until the night of the 30th, after the army had made two marches, that General Meade became satisfied that Lee, apprised of his movement, had loosed his hold on the Susquehanna and was concentrating his forces east of the South Mountain to meet him. But when and where the shock of battle, which was now seen to be imminent, would take place it was impossible to tell. Under these circumstances, he set about to select a position on which, by a rapid movement of concentration, he might be prepared to receive battle on advantageous terms. With this view, the general line of Pipe Creek, on the dividing ridge between the Monocacy and the waters running into the Chesapeake Bay, was selected as a favorable position, though its ultimate adoption was held contingent on developments that might arise. Accordingly, orders were issued on the night of the 30th for the movements of the different corps on the following day: the Sixth Corps, forming the right wing of the army, was ordered to Manchester in rear of Pipe Creek; headquarters and the Second Corps to Taneytown; the Twelfth and Fifth corps, forming the centre, were directed on Two Taverns and Hanover, somewhat in advance of Pipe Creek; while the left wing, formed of the First, Third, and Eleventh corps under General Reynolds, as it was closest to the line of march of the enemy, was thrown forward to Gettysburg, towards which, as it happened, Lee was then heading.