12. The Battle of Chantilly opened the door for Lee’s first invasion of Maryland in 1862
Following his disastrous defeat at the 2nd Battle of Bull Run, Union General John Pope wanted to withdraw his shattered Army of Virginia into the defenses surrounding Washington. Robert E. Lee allowed his enemy to withdraw as far as Centerville, Virginia, where Pope received orders from Washington to attack Lee’s army, which remained on the field around Manassas. Pope was reinforced with additional troops drawn from the Union forces on the Virginia Peninsula below Richmond. Union General in Chief Henry Halleck believed with the additional troops, Lee’s nearly exhausted army could be dealt a punishing blow. Pope did not agree, hesitated, and then learned of a flanking movement by Stonewall Jackson’s troops. If successful, Jackson’s maneuver would put Pope between Jackson and Lee. Jackson would also be between Pope and the safety of the Washington defenses.
Pope countermanded his orders, issued in obedience to Washington, to prepare for an attack. Instead, he ordered a general retreat of his forces to Washington. He did order infantry and cavalry units forward, with supporting artillery, to block the roads being used by Lee and Jackson to entrap him. On September 1, 1862, two days after his defeat at Bull Run, Pope began his retreat. Meanwhile the forces he sent forward encountered Jackson’s Second Corps of the Army of Northern Virginia near Chantilly Plantation at a place known as Ox Hill. The area swarmed with Confederate and Union Cavalry, which engaged each other in skirmishing throughout the morning. By mid-afternoon, the Union divisions ordered forward by Pope arrived on the battlefield. Along with them arrived a heavy thunderstorm, soaking the cartridges carried by the infantry, and rendering their muskets useless.