In the meantime, Longstreet had reached Thoroughfare Gap at about 3 p. m. of the same day to find his way blocked by Federal troops under Ricketts. Outmaneuvering his opponent by way of Hopewell Gap, he forced him to fall back to Gainesville. That night, without informing Pope of their intentions, King and Ricketts decided to move towards Manassas. This enabled Longstreet to effect an easy junction with Jackson in the afternoon of the following day.

THIRD PHASE—MAIN BATTLE, AUGUST 29-30.

When Pope learned of the engagement of Groveton he mistakenly decided that King had met the head of Jackson’s column in retreat. Confident of success, he ordered a concentration of his leg weary troops to crush the Confederate force. Sigel and Reynolds were to attack at dawn, reinforced by Heintzelman and Reno. McDowell and Porter were ordered to reverse their course and push toward Gainesville in an effort to cut off Jackson’s retreat. The text of this order known as the “Joint Order,” which was received about noon, reads as follows:

[High-resolution Map]

Headquarters Army of Virginia Centreville, August 29, 1862.

Generals McDowell and Porter:

You will please move forward with your joint commands toward Gainesville. I sent General Porter written orders to that effect an hour and a half ago. Heintzelman, Sigel, and Reno are moving on the Warrenton turnpike, and must now be not far from Gainesville. I desire that as soon as communication is established between this force and your own the whole command shall halt. It may be necessary to fall back behind Bull Run at Centreville to-night. I presume it will be so, on account of our supplies....

If any considerable advantages are to be gained by departing from this order it will not be strictly carried out. One thing must be had in view, that the troops must occupy a position from which they can reach Bull Run to-night or by morning. The indications are that the whole force of the enemy is moving in this direction at a pace that will bring them here by to-morrow night or the next day. My own headquarters will be for the present with Heintzelman’s corps or at this place.

Jno. Pope, Major-General, Commanding.

Prior to the receipt of the “Joint Order,” Porter had reversed his course to Centreville and had moved as far as Dawkin’s Branch, located about 3 miles from Gainesville. Finding the Confederates strongly posted in his front, he deployed a brigade of his leading division and waited. McDowell, who arrived shortly thereafter, showed him a dispatch he had received a few minutes before from Buford, who commanded the Union cavalry on the right. The dispatch stated that 17 regiments, 1 battery, and 500 cavalry had passed through Gainesville about 8:45 a. m. This was the advance of Longstreet’s command which had left Thoroughfare Gap early that morning and now, followed by heavy reinforcements, was moving into position on Jackson’s right (Porter’s front).

This information, the generals felt, had not reached Pope. After a conference, it was decided that in face of this new development they would take advantage of the latitude the order granted: McDowell would move towards Groveton, while Porter would remain in the vicinity of his present position.

The relative quiet in this sector was in sharp contrast to the heavy fighting now taking place along Jackson’s front. With about 18,000 infantry and 40 guns, Jackson had taken up a position along an unfinished railroad bed which extended from near Sudley Springs 2 miles southwesterly to Groveton. The grades and cuts of this road provided ready-made entrenchments and formed a very strong position. There, shortly after sunrise, Sigel’s and Reynolds’ columns were seen at a distance deploying for the attack. About 7 a. m., the Federal batteries opened fire. By 10:30 a. m., a number of sharp skirmishes had taken place, but no general assault had been made. About this time Federal reinforcements of Reno and Kearny reached the field. It was not until 2 p. m., however, that the battle reached its height. All afternoon in violent but uncoordinated attacks, blue columns gallantly assaulted Jackson’s line. At one point the Confederate left was pushed back dangerously near the breaking point, but the gray line steadied and held. Towards dusk, King’s division, of McDowell’s corps, arrived in time to take part in the action, engaging a part of Longstreet’s command which was then advancing on a reconnaissance.