The Battle of Chantilly (or Ox Hill, the Confederate name) took place on September 1, 1862, in Fairfax County, Virginia, as the concluding battle of the Northern Virginia Campaign of the American Civil War.
By the morning of August 31, Pope seemed to be losing his grasp on command of his force. The defeat at Second Bull Run seemed to have shattered his nerve and Pope was unsure what to do next; he knew Washington wanted an attack but he feared Lee might strike first and shatter his reforming force before it was ready to fight again. Calling a conference of his corps commanders—something he had been loath to do previously in the Virginia Campaign—in his Centreville headquarters, Pope agreed with their decision to retreat further into the Washington defenses. But a message from General-in-Chief Henry W. Halleck directed him to attack and he ordered an advance on Lee's forces on the Manassas field.
Lee, however, had already set in motion his own plan that would rob Pope of the initiative to attack. Lee directed Maj. Gen. Thomas J. "Stonewall" Jackson to march his troops around Pope's right flank to get behind the Union position at Centreville. Leading the way and scouting for any Union blocking force was Confederate cavalry under the command of Maj. Gen. J.E.B. Stuart. Maj. Gen. James Longstreet's command would remain in place for the day to deceive Pope into believing that Lee's entire force remained in his front, while Jackson's command made their flanking march, north and then east, to take strategically important Germantown, Virginia, where Pope's only two routes to Washington—the Warrenton Pike (modern U.S. Route 29) and the Little River Turnpike (modern U.S. Route 50)—converged. Jackson's men, hungry and worn, moved slowly and bivouacked for the night at Pleasant Valley, three miles northeast of Centreville. As Pope settled down for the night on August 31, he was unaware that Lee was on the verge of turning his flank.
During the night two events occurred that would force Pope to change his mind. A staff officer arrived from the Germantown position to report that a heavy force of cavalry had shelled the intersection before retreating. Fortunately for Lee and Stuart, Pope dismissed the cavalry as little more than a patrol. But when, hours later, two Union cavalrymen reported seeing a large mass of infantry marching east down the Little River Turnpike, Pope realized that his army was in danger. He countermanded actions preparing for an attack and directed the army to retreat from Centreville to Washington; he also sent out a series of infantry probes up the roads that Lee might use to reach his troops as they pulled back.
On the morning of September 1, Pope ordered Maj. Gen. Edwin V. Sumner to send a brigade north to reconnoiter; the army's cavalry was too exhausted for the mission. But at the same time, he continued his movement in the direction of Washington, sending McDowell's corps to Jermantown (on the western border of modern day Fairfax City), where it could protect an important intersection the army needed for the retreat. And he sent two brigades of Maj. Gen. Jesse L. Reno's IX Corps, under the command of Brig. Gen. Isaac Stevens, to block Jackson. Maj. Gen. Philip Kearny's division followed later that afternoon.
Jackson resumed his march to the south, but his troops were tired and hungry and made poor progress as the rain continued. They marched only 3 miles and occupied Ox Hill, southeast of Chantilly Plantation, where they encountered Stevens's three brigades about 3 p.m. Despite being outnumbered, Stevens choose to attack across a grassy field against Brig. Gen. Alexander Lawton's division in the Confederate center. The Union attack was initially successful, routing one brigade and the flank of another, but was driven back following a counterattack by Jubal Early's brigade. Stevens was killed during this attack about 5:00 pm by a shot through his temple.
Kearny arrived about this time with his division and deployed David B. Birney's brigade on Stevens' left, ordering it to attack. Briney managed to maneuver close to the Confederate line but his attack stalled in hand-to-hand combat with A.P. Hill's division. Kearny mistakenly rode into the Confederate lines during the battle and was killed. As Kearny's other two brigades arrived on the field, Birney withdrew to the southern side of the farm fields, ending the battle.
That night, Longstreet arrived to relieve Jackson's troops and to renew the battle in the morning. The Union army withdrew to Germantown and Fairfax Court House that night.
The fighting was tactically inconclusive, but Jackson's turning movement was foiled and he was unable to block the Union retreat or destroy Pope's army. Two key Union generals were killed. Pope, recognizing the attack as an indication of continued danger to his army, continued his retreat to the fortifications around Washington, D.C.. Lee began the Maryland Campaign, including the Battle of Antietam, after Pope retreated out of Virginia. The Army of the Potomac, under Maj. Gen. George B. McClellan, absorbed the forces of Pope's Army of Virginia, which was disbanded as a separate army.
The site of the battle, once rural farmland, is now surrounded by suburban development in Fairfax County. The intersection of the modern thoroughfares of Route 50 (also known as Lee-Jackson Memorial Highway) and State Route 7100 (also known as Fairfax County Parkway) intersect near the location of the battle. A 4.8 acre (19,000 m²) memorial park, the Ox Hill Battlefield Park, lies adjacent to the Fairfax Towne Center shopping area, and includes the site of the battle. The park is under the jurisdiction of the Fairfax County Park Authority; in January 2005, the Authority approved a General Management Plan and Conceptual Development Plan that sets forth a detailed history and future management framework for the site.