The two armies confronted each other with that river between. Lee moved by his left flank up the river while Pope kept pace with him, alertly meeting him at every available point of crossing, with his army in discouragingly strong positions, and prepared to resist to the utmost any attempt the Confederate general might make to force a crossing.
To Lee this was a lamentable waste of time, while to Pope it was a matter of hourly gain in strength. For while Lee already had with him all the forces that he could hope to concentrate in that quarter, regiments and brigades and divisions were constantly pouring forward from Washington to strengthen Pope's command.
Finally Lee succeeded in outwitting his adversary. At a place near Warrenton Springs he came to a halt and made ostentatious demonstrations of an intention to force a crossing of the river at that point. Pope stood ready to meet him, with all his army strongly posted, and with hourly strengthening field works to make the assault of the Confederates the more difficult and the more perilous.
But Lee in fact had no intention of joining battle on such unequal conditions and risking the fate of his campaign upon his ability to carry such a position, so strongly defended. While occupying Pope's attention there with a simulated purpose of forcing the fords he resorted to that tactical device which served him so often and so well later in the war. He detached Jackson, sending him with a strong force to march around Bull Run Mountain, cross through Thoroughfare Gap, and threaten Pope's depots at Manassas and his lines of communication north and south of that now historic point.
Jackson's movement was completely concealed and altogether successful. On the twenty-sixth of August he fell like a thunderbolt upon Pope's depots at Manassas and captured them. Meanwhile, under Lee's orders, Longstreet was following Jackson, and on the twenty-ninth he formed a junction with him at or near the point where the first important battle of the war had been fought.
But Pope had not been idle or inattentive during these pregnant days. As soon as Jackson's descent upon his supply depots was made known to him, he abandoned his position on the Rappahannock and fell back to try conclusions on the historic field of Manassas. Having received still further reinforcement from McClellan, his army now slightly exceeded Lee's in numbers and considerably exceeded it in other elements of strength. Accordingly, being a commander of great enterprise and vigor, he at once assailed Lee at Manassas in full force. For two days he hurled his heavy battalions upon the Confederates, severely taxing and testing their resisting power. For these were armies of veteran, battle-seasoned soldiers that were fighting each other now, and not the raw levies of a year before. They fought with order and system and their minds were open to no such panic impulses as those that had put McDowell to rout and reduced what had been placed under his command as an army to the condition of an insanely frightened mob.
But on the other hand the Southerners were commanded now not by a pair of inexperienced ex-captains of the Engineer Corps, but by Robert E. Lee himself, with Stonewall Jackson and James Longstreet and R. S. Ewell and the two Hills for his lieutenants.
The attack was determined; the defense obstinate; the fighting heroic; the result bloody in an extreme degree.
The field was contested for two days with a heroic stubbornness on either side which showed clearly how great a change had been wrought in the conditions of the war by the disciplining of the troops, by their experience in the brutally bloody work of war, and by the training such experience had given to their officers.
The end of it was that Lee drove Pope across Bull Run and back to Centreville. Immediately he followed up his victory as Johnston and Beauregard had not done a year before on the same field. He turned the position at Centreville and compelled Pope to retreat hurriedly, but in tolerably good order, upon Washington.