them, gave detailed instructions to those who had charge of the advanced positions (at Fairfax Court-House and Fairfax Station) touching their respective lines of retreat on Bull Run
, in case they should be menaced by a combined serious movement of the enemy with largely superior forces.
The substance of those instructions was embodied, with minute details, in a Special Order, No. 100, from the Adjutant-General
's office, which was the order literally executed on the 17th of July.
This is one of the most remarkable instances in military history, of an order providing fully and precisely, nearly a month in advance, for all the exigencies of a strategic movement, remotely contingent upon the operations of an enemy.
, upon the near approach of the forces confronting him, was to retire slowly on Centreville
, by the turnpike, then to Mitchell's Ford, drawing the enemy after him to that point, which was the only portion of General Beauregard
's line yet fortified.
, from Sangster
's Crossroads and vicinity, was to follow the line of the railroad over a rather rough and difficult country road to Union Mills Ford, where the position was naturally strong and offered good cover to his men. The intermediate fords, McLean
's and Blackburn
's, were at that time occupied by Jones
's and Longstreet
's brigade, which had been watching the fords of the Occoquan
and the approaches on the right, was now held in reserve, a short distance in rear of Union Mills Ford, to act according to circumstances.
A small force of infantry guarded the stone bridge, on the extreme left, where the turnpike from Alexandria
, through Fairfax Court-House and Centreville
, crosses Bull Run
, on its way to Warrenton
The works, armed with naval guns, were manned by the seamen already alluded to, and also by a force of the State
militia, which Governor Letcher
had called out, at General Beauregard
During the latter days of June and the first fortnight of July, thorough reconnoissances were made of the whole region of country likely to become the theatre of war in that quarter, either for a defensive or offensive campaign.
In these General Beauregard
had the effective aid of Colonel Williamson
and Captains D. B. Harris
and Walter H. Stevens
, of the Engineers
And it may be of interest to mention here, that the reconnoissances we speak of included the surroundings of Leesburg
and the passes westward, as well as the entire square between Difficult Run