The AoP-Acting on Good Intelligence

[whitworth]

On June 24th, 1863, the movement of the Army of Northern Virginia was observed by the Signal Corps, atop the Maryland Heights opposite Harper's Ferry, by telescope.


MARYLAND HEIGHTS SIGNAL STATION,
June 24—1O.40 a. m.
General Slocum
Large trains are crossing at Sharpsburg. Artillery and general trains are passing near Charlestown toward Shepherdstown.
FISHER,Lieutenant, Signal Officer.

General Hooker, still in command of the AoP, started moving the army across two pontoon bridges and over the Potomac River near Leesburg,Virginia, the next day, June 25.

General Stuart, who had just been engaging Union cavalry, protecting Lee's backdoor, the gaps in the Blue Ridge Mountains, started his move to Pennsylvania, east through the Bull Run Mountains. The move also began on June 25, some thirty miles south of the Army of the Potomac's crossing of their namesake river.
The Army of the Potomac not only had a headstart on Stuart, Stuart found his way blocked at the gaps through Bull Run Mountains.