The Second Battle of Bull Run was fought on August 29 and 30, 1862, in Virginia. The battlefield, situated about 30 miles west of Washington DC, included some of the battlefield of the First Bull Run, fought the previous summer. The Union's general plan was to move McClellan's Army of the Potomac by water up Chesapeake Bay to a position north of Fredericksburg, where it would merge with a new army under Pope and overwhelm Lee's Confederate troops through superior numbers. Lee recognized the danger and decided to attack before the two Union armies could be combined against him. In order to draw John Pope’s Union armyinto battle, Thomas Jackson ordered an attack on a Federal column passing across his front on the Warrenton Turnpike on August 28. The fighting lasted several hours and resulted in a stalemate. Pope became convinced that he had trapped Jackson and concentrated the bulk of his army against him. On August 29, Pope launched a series of assaults against Jackson’s position along an unfinished railroad grade. The attacks were repulsed with heavy casualties on both sides. Later, Confederate reinforcements under James Longstreet arrived on the field and took a position on Jackson’s right flank. On August 30, Pope renewed his attacks, seemingly unaware that the opposition had been strengthened. When massed Confederate artillery devastated a Union assault, 28,000 Confederate men counterattacked in the largest simultaneous mass assault of the war. The Union left flank was crushed and the army driven back to Bull Run. At Centreville, Pope's army was at last reinforced by elements of the Army of the Potomac. Lee, however, was on the offensive. Almost immediately after the Second Battle of Bull Run had ended, Lee sent Jackson on a sweep that would threaten the highway between Centreville and Washington. He himself followed along a different route. On September 1, the federal forces were able to halt Jackson's advance, but Lee's army arrived soon thereafter. The next day, Halleck ordered the Union armies to return to position behind the defenses of Washington, which is where they had started prior to the First Battle of Bull Run the previous July. Lee had expelled the Union from Virginia.