The sound of firing at Thoroughfare Gap was audible, and he knew that Longstreet's division of Lee's army was hotly engaged with a force which, now that it was too late, had been sent to hold the gorge.

It was nearly sunset before Pope brought up his men to the attack.

Jackson did not stand on the defensive, but rushed down and attacked the enemy--whose object had been to pass the position and press on--with such vigor that at nine o'clock they fell back.
An hour later a horseman rode up with the news that Longstreet had passed the Gap and was pressing on at full speed, and in the morning his forces were seen approaching, the line they were taking bringing them up at an angle to Jackson's position.

Thus their formation as they arrived was that of an open V, and it was through the angle of this V that Pope had to force his way.

Before Longstreet could arrive, however, the enemy hurled themselves upon Jackson, and for hours the Confederates held their own against the vast Federal army, Longstreet's force being too far away to lend them a hand.