From this office in Richmond Lee watched these formidable preparations for invading the South with no little apprehension. He knew that the Confederates had only about 50,000 available troops with which to oppose McClellan's great army and had the Union commander been aware of this he might have moved straight against the city and swept its defenders from his path. But McClellan always believed that he was outnumbered and on this occasion he wildly exaggerated his opponents' strength. In fact, he crept forward so cautiously that the Confederates, who had almost resigned themselves to losing the city, hastened to bring up reënforcements and erect defensive works of a really formidable character. The best that was hoped for, however, was to delay the Union army. To defeat it, or even to check its advance, seemed impossible, and doubtless it would have proved so had it not been for the brilliant exploits of the man who was destined to become Lee's "right hand." This man was General Thomas Jonathan Jackson, who had earned the nickname of "Stonewall" at Bull Run and was at that time in command of about 15,000 men guarding the fertile Shenandoah Valley, the "granary of Virginia." Opposing this comparatively small army were several strong Union forces which were considered amply sufficient to capture or destroy it, and McClellan proceeded southward, with no misgivings concerning Jackson. But the wily Confederate had no intention of remaining idle and McClellan's back was scarcely turned before he attacked and utterly routed his nearest opponents. A second, third and even a fourth army was launched against him, but he twisted, turned and doubled on his tracks with bewildering rapidity, cleverly luring his opponents apart; and then, falling on each in turn with overwhelming numbers, hurled them from his path with astonishing ease and suddenly appeared before Washington threatening its capture. Astounded and alarmed at this unexpected peril, the Federal authorities instantly ordered McDowell's corps of 40,000 men, which was on the point of joining McClellan, to remain and defend the capital. This was a serious blow to McClellan who had counted upon using these troops, though even without them he greatly outnumbered the Confederates. But the idea that he was opposed by an overwhelming force had taken such a firm hold on his mind that he was almost afraid to move, and while he was timidly feeling his way General Joseph Johnston, commanding the defenses at Richmond, attacked his advance corps at Seven Pines, May 31, 1862. A fierce contest followed, during which Johnston was severely wounded, and Jefferson Davis, who was on the field, promptly summoned General Lee to the command.