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.