On July 16, 1861, the new Union volunteer army under Brig. Gen. Irvin McDowell marched from Washington DC toward the Confederate army under Gen. Pierre G. T. Beauregard, drawn up behind Bull Run creek west of Centreville. Beauregard's men defended the strategic railroad junction at Manassas, just west of the creek. On July 17, McDowell sent a small force across Bull Run at Blackburn's Ford to test the Confederate defenses. A brief skirmish ensured, with light casualties and little result. McDowell made plans to attack the north or left end of Beauregard's line, while making a simultaneous demonstration where the Warrenton Turnpike crossed the creek at a stone bridge. Early on July 21, two of McDowell's divisions crossed at Sudley Ford and attacked the Confederate left flank on Matthews Hill. Fighting raged throughout the morning as Confederate forces were driven back to Henry Hill and more Union brigades crossed Bull Run. In the afternoon, Confederate reinforcements arrived via railroad from Gen. Joseph Johnston's army in the Shenandoah Valley, among them a brigade of Virginians under Brig. Gen. Thomas J. Jackson. Jackson organized a defense of Henry Hill bolstered by artillery. McDowell also ordered more infantry and artillery to Henry Hill, where the fiercest fighting of the new war occurred. Additional Confederate reinforcements broke the Union right flank, and Jackson held his ground on Henry Hill "like a stone wall." Under counterattack and with no reinforcements, the Federals retreated which soon deteriorated into a complete rout. The next day, the shattered Union army reached the safety of Washington and the first battle of the war was over.