Lee started north to crush Pope before McClellan should reach him. Pope had but 50,000 men against Lee's 80,000, and fell back across the Rappahannock. Lee sent Jackson on a far detour, via Thoroughfare Gap, to get into his rear and cut his communications. Jackson moved rapidly around to Manassas--one of the most brilliant exploits in all the war--and destroyed Pope's immense supply depot there. On August 29th he was attacked by Pope near the old battlefield of Bull Run. The first day's fight was indecisive, but Confederate re-enforcements under Longstreet arrived in time to join in the battle of the next. McClellan was in no hurry to re-enforce his rival, but proposed "to leave Pope to get out of his scrape as he might." Toward sunset in the battle of the 30th, Longstreet's column, doubling way around Jackson's right and Pope's left, made a grand charge, taking Pope straight in the flank. Porter's corps--the Fifth--part of McClellan's army, stood in the "bloody angle" of cross-fire. His loss was dreadful--2,000 out of 9,000. Pope was compelled to retire to Centreville. An engagement at Chantilly, September 1st, forced a further retreat to Washington. Pope resigned, and his army was merged in the Army of the Potomac, McClellan commanding all. [Illustration: Portrait.] General Thomas J. ("Stonewall") Jackson. Lee now invaded Maryland with 60,000 men. Already the alarmed North heard him knocking at its gates. Hastily re-organizing the army, McClellan gave chase. Leaving a force to hold Turner's Gap in South Mountain, Lee pushed on toward Pennsylvania. By the battle of South Mountain, September 14th, Hooker got possession of the gap, and the Union army poured through. Seeing that he must fight, Lee took up a position on Antietam Creek, a few miles north of Harper's Ferry. Jackson had just received the surrender of the latter place, with 11,000 prisoners, and now hurried to join Lee. By the night of September 16th, the two armies were in battle array on either side of the creek. To the rear of the Confederate left lay a cultivated area encircled by woods, a cornfield in its centre. At dawn on the 17th, Hooker opened the battle by a furious charge against the Confederate left, and tumbled the enemy out of the woods, across the cornfield, and into the thickets beyond, where he was fronted by Confederate reserves. The carnage was terrific. Re-enforcements under Mansfield were sent to Hooker, but driven back across the cornfield. Mansfield was killed and Hooker borne from the field wounded, Sumner coming up barely in time to prevent a rout. Once more the Confederates were pushed through the cornfield into the woods. Here, crouching behind natural breastworks--limestone ridges waist-high--the southern ranks delivered so hot a fire as to repulse Sumner's men. Thus, all the morning and into the afternoon the tide of battle surged back and forth through the bloody cornfield, strewn with wounded and dead.