Confederate Major General Thomas J Stonewall Jackson took his troops through Thoroughfare Gap on August 26th 1862, on his way to raid the Union supply depot at Manassas Junction. The next day Union Major General Irwin McDowell headed for Manassas in pursuit. To protect his left flank he sent the 1st New Jersey Cavalry and Brigadier General James B Ricketts’ Brigade towards Thoroughfare Gap. Ricketts’ halted about 6 miles east of the Gap at Gainesville, Virginia, sending the Cavalry to occupy the Gap. At the same time Confederate Major General James Longstreet’s Corps was following Jackson, coming toward the Gap from the West.
On the morning of August 28th 1862 the 1st New Jersey Cavalry encountered Longstreet’s lead troops while they were falling trees to block the road on the East side of the Gap. Word was sent to Ricketts to bring up his troops, but he moved slowly, only making it as far as Haymarket still 3 miles from the Gap at 2 pm. At that point Longstreet had pushed the Union Cavalry out of the Gap.
Longstreet moved his men to the high ground on either side of the Gap and then moved to outflank the Union position. The 9th Georgia Infantry part of Confederate Colonel George T Anderson brigade moved to Chapman’s Mill on the East side of the Gap and attacked the 11th Pennsylvania. South of the Gap the 2nd and 20th Georgia met the 13th Massachusetts and drove them back down the steep slopes. Holding the Gap, Confederate Colonel Evander M Law’s Brigade moved against the Union right at the same time Confederate Brigadier General Cadmus M Wilcox took 3 Brigades North through Hopewell Gap to outflank the Union and hit them in the rear. With the Union position becoming untenable Ricketts ordered the men to fall back to Gainesville, leaving the Gap before Wilcox got into position to cut him off.
This was a rather small action, but opened up the way for Longstreet to join his Corps with Jackson’s leading to the Union loss at the Second Battle of Manassas.