On August 28–30, 1862, the Confederate Army of Northern Virginia commanded by General Robert E. Lee defeated Union Major General John Pope's Army of Virginia at the Second Battle of Bull Run or Second Manassas. Pope retreated to Centreville, Virginia where he considered having his force retreat into the defenses of Washington, D.C. Since Pope's men retreated and reorganized in seemingly good order, Major General Henry W. Halleck, then Union Army General-in-Chief, ordered Pope to attack Lee. Lee had not ordered an immediate pursuit of Pope's army because the Confederates were exhausted from three weeks of marching and the battle and were low on ammunition and supplies. On the next day, Lee ordered Major General Thomas J. "Stonewall" Jackson to outflank the Union Army and get his force between Pope's men and Washington, D.C. This led to the Battle of Chantilly or Ox Hill in Fairfax County, Virginia on September 1. Two Union Army divisions held off the Confederate force as a severe thunderstorm hampered continued fighting. After the fighting ceased, the Union forces withdrew first to Jermantown, Virginia and Fairfax Court House, Virginia and then into the Washington, D.C. defenses. This cleared the way for the Maryland Campaign, Lee's first invasion of the North.