<P> To the west, Chinn Ridge had been occupied by Col. Oliver Otis Howard's brigade from Heintzelman's division . Also at 4 p.m., two Confederate brigades - Col. Jubal Early's, which had moved from the Confederate right, and Brig. Gen. Edmund Kirby Smith's (commanded by Col. Arnold Elzey after Smith was wounded), which had just arrived from the Shenandoah Valley--crushed Howard's brigade . Beauregard ordered his entire line forward . At 5 p.m. everywhere McDowell's army was disintegrating . Thousands, in large and small groups or as individuals, began to leave the battlefield and head for Centreville . McDowell rode around the field trying to rally regiments and groups of soldiers, but most had had enough . Unable to stop the mass exodus, McDowell gave orders for Porter's regular infantry battalion, near the intersection of the turnpike and Manassas - Sudley Road, to act as a rear guard as his army withdrew . The unit briefly held the crossroads, then retreated eastward with the rest of the army . McDowell's force crumbled and began to retreat . </P> <P> (Further map details, see: Additional Map 8, Additional Map 9, Additional Map 10, Additional Map 11 and Additional Map 12 .) </P> <P> The retreat was relatively orderly up to the Bull Run crossings, but it was poorly managed by the Union officers . A Union wagon was overturned by artillery fire on a bridge spanning Cub Run Creek and incited panic in McDowell's force . As the soldiers streamed uncontrollably toward Centreville, discarding their arms and equipment, McDowell ordered Col. Dixon S. Miles's division to act as a rear guard, but it was impossible to rally the army short of Washington . In the disorder that followed, hundreds of Union troops were taken prisoner . Wagons and artillery were abandoned, including the 30 - pounder Parrott rifle, which had opened the battle with such fanfare . Expecting an easy Union victory, the wealthy elite of nearby Washington, including congressmen and their families, had come to picnic and watch the battle . When the Union army was driven back in a running disorder, the roads back to Washington were blocked by panicked civilians attempting to flee in their carriages . </P> <P> Since their combined army had been left highly disorganized as well, Beauregard and Johnston did not fully press their advantage, despite urging from Confederate President Jefferson Davis, who had arrived on the battlefield to see the Union soldiers retreating . An attempt by Johnston to intercept the Union troops from his right flank, using the brigades of Brig . Gens . Milledge L. Bonham and James Longstreet, was a failure . The two commanders squabbled with each other and when Bonham's men received some artillery fire from the Union rear guard, and found that Richardson's brigade blocked the road to Centreville, he called off the pursuit . </P>

Who fired the first shot at the battle of bull run