Dowell also joined it on the evening of the 18th. It still lay in camp on the two following days, Friday, the 19th, and Saturday, the 20th. General McDowell devoted that time to getting all possible information about the roads to Manassas, the condition of the several crossings of Bull Run by bridges and fords, and the distribution of the enemy's forces, in order to formulate his plans for further operations. What was ascertained regarding the natural and artificial difficulties (abattis, rifle-pits, and batteries in position) of effecting a crossing of Bull Run on the direct line to the Junction, made him abandon his original plan of turning Beauregard's right flank from the south and decide to attempt a flanking movement from the north, concealed by a front attack. He informed his division commanders accordingly on the evening of the 18th; but the engineers, not getting through with the necessary reconnoissances before the afternoon of Saturday, the 20th, the execution of the modified plan was not attempted before the next day.
On Saturday night the division commanders assembled at headquarters to receive their final instructions. The Warrenton turnpike formed the main street of Centreville and ran thence directly southwest to Bull Run, which it crossed on a solid stone bridge of two arches, to which Beauregard's left flank extended. General Tyler was ordered to move with his division over the turnpike to the bridge, a distance of three miles and a half, and there make a feint attack. Hunter and Heintzelman were ordered to make a circuitous night march northward, cross Bull Run at Sudley Springs, between two and three miles above the stone bridge, follow the stream down to the latter, and, taking from the rear the armed fortifications which the enemy were supposed to have at that point, open the way for the crossing of Tyler's division. The three divisions should then jointly attack the rebel left. Miles's division was to remain in reserve at Centreville. Richardson's brigade was to threaten Blackburn's Ford.
