Battle of Chantilly - Background

Background

Further information: Confederate order of battle, Union order of battle

Defeated in the Second Battle of Bull Run on August 30, Union Maj. Gen. John Pope ordered his Army of Virginia to retreat to Centreville. The movement began after dark, with Maj. Gen. Irvin McDowell's III Corps providing cover. The army crossed Bull Run and the last troops across, Maj. Gen. Franz Sigel's I Corps, destroyed Stone Bridge behind them. Gen. Robert E. Lee decided not to press the advantage gained that day, largely because he knew his Army of Northern Virginia was exhausted from two weeks of nearly constant marching and nearly three days of battle, so the Union retreat went unmolested. Lee's decision also allowed the Army of Virginia's II Corps, under Maj. Gen. Nathaniel P. Banks, to consolidate with the bulk of Pope's army, marching in from Bristoe Station, where they had been guarding the army's trains. More importantly, Lee's decision bought time for the Union to push to the front the Army of the Potomac's II, V, and VI Corps, which had been brought from the Peninsula and—much to Maj. Gen. George B. McClellan's dismay—placed under Pope's command.

By the morning of August 31, Pope began to lose his grasp on command of his army. 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 destroy 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.