General Lee planned an attack on Pope immediately before his arrival on the Rapidan. R. H. Anderson's division was ordered up from Richmond, and the plan of campaign was to be carried out on the 18th by crossing the Rapidan and turning Pope's left. But a letter from General Lee detailing the movements of the cavalry fell into Pope's hands by the capture of Stuart's adjutant-general, and Pope, thus apprised of the plans of his adversary, on the 17th fell back behind the Rappahannock to a much stronger position. The lost dispatch had broken up the plans for the expected battle, and Lee put his two corps in position on the south bank of the Rappahannock, Longstreet on the right and Jackson on the left.
Now, sure that he could with safety collect all his army on the Rappahannock, General Lee wrote the President for the divisions of D. H. Hill and McLaws, and General Hampton's cavalry. On the 19th, the President, fearing that Richmond would be endangered, telegraphed General Lee that until movements of the enemy were more developed he would retain those commands before the capital. Finally, on the 24th, Lee wrote Mr. Davis that he had intercepted a letter from General Pope to General Halleck (commander-in-chief of the United States armies), dated August 20th, stating his whole force for duty at 45,000, independent of Burnside, and revealing his plan to hold Lee in check until McClellan could come up from the lower Rappahannock. Thus General Lee was put in possession of General Pope's plans and formed his own accordingly. He wrote the President that he wished his whole army immediately, and all available troops, and added: "Hampton's cavalry I particularly require." Richmond, he wrote, must rely upon her defenses and field batteries. On the 26th, McLaws and D. H. Hill and Hampton were ordered to Lee, and Mr. Davis wrote him: "Confidence in you overcomes the view that otherwise would be taken of the exposed condition of Richmond, and the troops retained for the defense of the capital are surrendered to you on a renewed request." Neither of these commands was able to reach Lee, however, until immediately after the conflicts on the Rappahannock and the great struggle at Manassas. The fords on the Rappahannock were too full for the crossing of the army, and too strongly defended by Pope's artillery.
Several affairs occurred during the five days Lee was detained on the right bank. In one of these Gregg's brigade was moved up to support a battery, and subjected to a severe shelling from a high hill on the left bank, losing several men killed and wounded. On August 23d a more serious affair occurred, in which the brigade of General Evans and Boyce's battery were engaged. The enemy had fortified a hill near the railroad bridge at Rappahannock Station, and on the right bank. Evans, supported by several batteries, was ordered to attack. The brigade moved up promptly against the fortified position, under a sharp counter fire, but before they reached charging distance the enemy retired, leaving his intrenching tools and other property, but taking guns and troops securely over the railroad bridge, which he fired and destroyed. Evans ordered Boyce to occupy the steep hill with his battery, and that gallant officer at once moved up but was immediately subjected to the fire of four batteries from commanding heights on the north bank. He was compelled immediately to withdraw, losing 8 killed and 14 wounded, and 7 horses killed. Lieut. William Monro of the battery was severely wounded. The brigade lost in this affair 27 killed and 84 wounded, a total of 111.
Without waiting for the arrival of the reinforcements from Richmond, General Lee began his movement around the right of General Pope on the 25th of August. Jackson was to move up the right bank of the river beyond the extreme right of Pope, cross beyond Waterloo and move on his railroad communications. Longstreet, after demonstrating in Pope's front, was to follow Jackson. The genius of Lee, Jackson and Longstreet was to determine the precise field and the essential conditions of the battle.
Jackson marched early on the 25th, crossed the upper branches of the Rappahannock, and camped at Salem, on the Manassas Gap railroad. On the 26th he turned due east, passed the Bull Run mountains through Thoroughfare gap, and by sunset was at Bristoe Station in Pope's immediate rear, and on his main railroad communication with Washington. The capture of Bristoe and Manassas Junction, with vast stores, followed.
Gregg's brigade, which had been under fire at Rappahannock bridge on the 21st, and further up the river on the Rappahannock hills on the 24th, crossed on the 25th at Henson's mill, and made a forced march of 24 miles that day up the Salem valley, and continued the march on the 26th "without wagons or baggage of any kind, turning to the right at Salem, through Thoroughfare gap, and sleeping at night in rear of our artillery in the road near Bristoe Station." General McGowan, whose report is quoted, continues:
The next morning we reached Manassas Junction, where the enemy, attempting to recapture it, were scattered with considerable loss. In the afternoon of that day the brigade returned from pursuit, to the junction, where three days' rations were issued from the vast supply of captured stores, and the men for a few hours rested and regaled themselves upon delicacies unknown to our commissariat, which they were in good condition to enjoy, having eaten nothing for several days except roasting ears taken from the fields near the road, and what was given by the generous citizens of the Salem valley to the soldiers as they hurried along in their rapid march.
At dark on the evening of August 27th (Wednesday), the brigade, in conjunction with that of General Thomas, was thrown out on the south side of Manassas Junction as the rear guard, and formed in line of battle facing the enemy, who had during the evening been fighting General Ewell near Bristoe Station. Standing under arms here we had a fine view of the magnificent conflagration caused by the burning of the sutler's and commissary stores, together with about 100 cars freighted with every article necessary for the outfit of a great army, all of which was set on fire about midnight and consumed.
About 2 o'clock in the morning of Thursday, the 28th, we silently retired from our picket lines in front of the enemy, and by the light of the smoldering ruins followed the division across Bull run at Blackburn's ford to Centreville. Here we rested a short time, and thence turned back toward Bull run, and moving by the Warrenton pike crossed the run again near the stone bridge. At this critical moment the enemy, falling back from the Rappahannock, caused doubtless by our flank movement, were coming down the turnpike from Warrenton, meeting us. We turned to the right, leaving the turnpike, and after going up the run a short distance, changed front and were drawn up in battle array along the line of the unfinished Independent railroad track, facing the turnpike along which the enemy was moving.
As Gregg's brigade took this position, brisk firing was heard upon the right, where the divisions of Taliaferro and Ewell were thrown by Jackson against the column of Pope's army coming up the Warrenton pike, expecting to find Jackson at Centreville. A severe engagement followed, the battle of Groveton, in which Ewell and Taliaferro were both wounded. About dark Gregg's brigade was hurried to the scene of action, but the firing soon after ceased.
Jackson resumed his place behind the railroad and lay the night of the 28th in perfect silence, doubtless to create the impression that he had retreated. Capt. J. F. J. Caldwell, of the First South Carolina, Gregg's brigade, who has written an admirable history of his brigade, and was himself a gallant participant in all of its hardships and glories, thus describes the night of the 28th of August: