dvanced brigades, on the night of the 16th of July, were made
aware, from these headquarters, of the impending movement,"]

On Tuesday the 16th, he notifies his advanced brigades. On Wednesday,
he sends a dispatch from Manassas, to Jefferson Davis, at Richmond,
announcing that the Union troops have assailed his outposts in heavy
force; that he has fallen back before them, on the line of Bull Run; and
that he intends to make a stand at Mitchell's Ford (close to Blackburn's
Ford) on that stream,--adding: if his (McDowell's) force is
overwhelming, "I shall retire to the Rappahannock railroad bridge,
saving my command for defense there, and future operations. Please
inform Johnston of this, via Staunton, and also Holmes. Send forward
any re-enforcements at the earliest possible instant, and by every
possible means."

In the meantime, however, Beauregard loses no time in advantageously
posting his troops. On the morning of the 18th of July, when the Union
advance enters Centreville, he has withdrawn all his advanced brigades
within the Rebel lines of Bull Run, resting them on the South side of
that stream, from Union Mills Ford, near the Orange and Alexandria
railroad bridge, up to the stone bridge over which the Warrenton Pike
crosses the Run,--a distance of some six to eight miles.

Between the Rebel left, at Stone Bridge, and the Rebel right, at Union
Mills Ford, are several fords across Bull Run--the general course of the
stream being from the North-West to South-East, to its confluence with
the Occoquan River, some twelve miles from the Potomac River.

Mitchell's Ford, the Rebel center, is about three miles to the
South-West of, and about the same distance North-East from, Manassas
Junction. But it may be well, right here, to locate all these fordable
crossings of the rocky, precipitous, and well-wooded Bull Run stream,
between the Stone Bridge and Union Mills Ford. Thus, half a mile below
the Stone Bridge is Lewis's Ford; half a mile below that, Ball's Ford;
half a mile below that, Island Ford; one and one-half miles below that,
Mitchell's Ford--one mile below that.

Blackburn's Ford; three-quarters of a mile farther down, McLean's Ford;
and nearly two miles lower down the stream, Union Mills Ford.

By Thursday morning, the 18th of July, Beauregard has advantageously
posted the seven brigades into which he has organized his forces, at
these various positions along his extended front, as follows:

At th