McDowell's purpose was to assail the Confederates on their extreme right, there making a feint as if to force a crossing of Bull Run at that point which he did not at all intend; to march his stronger battalions to his own right along roads substantially parallel with Bull Run; here and there to divert a force to the Bull Run line and make fighting there by way of preventing Confederate concentration at any point and finally to hurl all his force with irresistible fury upon the extreme left of the Confederate line, which he intended and confidently expected to turn and overwhelm with his superior numbers. It was McDowell's plan to deceive the Confederates as to his point of decisive attack, to keep them busy all along the Bull Run line and, late in the day, to envelop their left wing, crush it by superior force, capture the railroad and perhaps compel Beauregard's surrender for lack of a line of retreat. The plan worked well for a time. The attacks of McDowell's divisions upon the Confederate right and center were stoutly and successfully resisted at every point, but they were made with determination and they served their purpose of deceiving the Southern commander or at least of preventing him from withdrawing heavy forces from that part of the field for the defense of his left against the final and crushing assault which McDowell intended to make there, and in preparation for which he was all day moving his heaviest columns in that direction along roads not visible from the Confederate lines. When at last that assault was made, it found Beauregard inadequately prepared for it; but, with the determination and energy which were the dominant traits of his character, the Confederate general held his ground obstinately and hurriedly moved troops from the right to the left of his line. The fighting raged furiously at this critical point and for a considerable time its result was in doubt, with the chances strongly in favor of the Federals. Three times the tide of battle ebbed and flowed across the disputed field, both sides fighting with a courage and obstinacy that were scarcely to have been expected of troops so little inured to the work of war. When the struggle was at its fiercest, and at the moment when the promise of it seemed to be that the Federals would overwhelm and crush their sorely outnumbered adversaries, a strong detachment of Johnston's troops from the Valley, long delayed on their railroad journey, reached the field. Their orders were of the vaguest, but they plainly saw an overmastering Federal force pressing the Confederates very hard in their immediate presence. So, following the Napoleonic instruction to go to the point of heaviest firing the officers commanding the arriving Confederates went at once into the thick of the fight. It was the work of a brief time for these fresh men to envelop the advancing Federal right wing and crush it to pulp.