The battle continued until night (September 14th), and resulted in heavy loss on both sides, the brave General Reno, of the United States army, among others, losing his life.
Darkness put an end to the action, the Federal forces not having succeeded in passing the Gap; but, learning that a column of the enemy had crossed below and threatened him with an attack in flank, General Lee determined to retire in the direction of Sharpsburg, where Jackson and the forces cooeperating with him could join the main body of the army.

This movement was effected without difficulty, and Lee notices the skill and efficiency of General Fitz Lee in covering the rear with his cavalry.

The Federal army failed to press forward as rapidly as it is now obvious it should have done.

The head of the column did not appear west of the mountain until eight o'clock in the morning (September 15th), and, nearly at the same moment ("the attack began at dawn; in about two hours the garrison surrendered," says General Lee), Harper's Ferry yielded to Jackson.
Fast-riding couriers brought the welcome intelligence of Jackson's success to General Lee, as the latter was approaching Sharpsburg, and official information speedily came that the result had been the capture of more than eleven thousand men, thirteen thousand small-arms, and seventy-three cannon.

It was probably this large number of men and amount of military stores falling into the hands of the Confederates which afterward induced the opinion that Lee's sole design in invading Maryland had been the reduction of Harper's Ferry.
General McClellan had thus failed, in spite of every effort which he had made, to relieve Harper's Ferry,[1] and no other course remained now but to follow Lee and bring him to battle.