After Confederate Gen. Robert E. Lee's victory at Chancellorsville in May 1863, he led the Army of Northern Virginia west to the Shenandoah Valley, then north through central Maryland and across the Mason-Dixon Line into Pennsylvania, while Union Gen. George G. Meade, who replaced Gen. Joseph Hooker on June 28, led the Army of the Potomac in pursuit. Lee had proposed a second invasion of the North in May 1863, and Confederate President Jefferson Davis approved it. Federal generals grew suspicious when Confederate cavalry massed in Culpeper County, and on June 9 Union cavalry chief Gen. Alfred Pleasonton crossed the Rappahannock River and struck Gen. J.E.B. Stuart's cavalry corps at Brandy Station. Stuart fought to a draw, but the Federal cavalry gained confidence. As Lee began moving toward the Shenandoah Valley, he ordered Stuart to screen the movement by placing his cavalry between the armies while Pleasonton probed westward. That led to the battles of Aldie, Middleburg, and Upperville, mounted and unmounted cavalry clashes fought along this road from June 17 through 21. Although Union horsemen pushed west across the Loudoun Valley with the same aggressive spirit shown at Brandy Station, Stuart's screening tactics succeeded, blocking the Federals' way to Ashby's Gap while Lee's infantry passed down the Shenandoah Valley and into central Maryland, stealing a march on the Union army. Still stung by Southern newspaper criticism alleging surprises and defeats, Stuart decided in Loudoun Valley on a daring raid around the Union army into Maryland, but he lost touch with Lee for a week, and the decision proved fateful. Soon the Army of Northern Virginia crossed into Pennsylvania, where the Army of the Potomac finally found it at Gettysburg on July 1, beginning a battle that neither general had planned to fight there. Three days later, the defeated Confederates retreated, crossing the Potomac River into Virginia on July 14.