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Federal army, having crossed the
Potomac, was advancing northward, and that the head of the column had reached the
South Mountain.
As our communications with the
Potomac were menaced, it was resolved to prevent his further progress in that direction by cencentrating our army on the east side of the mountains.
Accordingly,
Longstreet and
Hill were directed to proceed from
Chambersburg to
Gettysburg, to which point
General Ewell was also instructed to march from
Carlisle.
The advance arrested.
Again, in his later and more carefully considered report, after the reports from all the different parts of the army had been received by him, he writes (p. 316): βThe advance upon
Harrisburg was arrested by intelligence received from a scout on the night of the 28th, to the effect, that the army of
General Hooker had crossed the
Potomac, and was approaching the
South Mountain.
In the absence of the cavalry it was impossible to ascertain his intentions; but to deter him from advancing further west and intercepting our communications with
Virginia, it was determined to concentrate the army east of the mountains.β
Acting under the impression produced by the scout's information, that the
Union army was moving westward towards
Hagerstown, on the line of his communications with
Virginia, it must have been a great surprise to him, when his leading divisions approached
Gettysburg, to find
Meade's advance was there ahead of him.
It had evidently been
General Lee's plan to operate west of the
South Mountain range, and keep
General Meade east of it, as the sending
Early east of it to threaten
Baltimore clearly indicates.
In case the
Union army crossed over in spite of his manoeuvres to prevent it, he relied upon the fact that the concentration of his army at
Gettysburg would place him nearer to
Baltimore than it, and unless his move was quickly responded to by it, he could interpose his army between Baltimore and
Washington on the one side and the
Union army on the other.
He was in error in supposing that contingency had arisen, though it appears from the fact on the morning of the 28th, three of the seven corps of the
Union army were in the
Catoctin Valley, near
Middleton, and one other at
Knoxville, with the passes in the
South Mountain heavily guarded, that it was
Hooker's purpose to have crossed over as
General Lee supposed he was doing.
