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 and then north through central Maryland into Pennsylvania as 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 moved toward the Shenandoah Valley, he ordered Stuart to screen the movement by placing his cavalry between the armies while Pleasonton probed westward, leading to the mounted and unmounted clashes at Aldie, Middleburg, and Upperville along this road from June 17 through 21. Although Union horsemen pushed west across the Loudoun Valley with new aggression, Stuart's screening succeeded, blocking the Federals from Ashby's Gap while Lee's infantry passed down the Shenandoah Valley and into central Maryland, stealing a march on the Union army. Stung by Southern newspaper criticism, Stuart decided in Loudoun Valley to make a daring raid around the Union army into Maryland, but he lost touch with Lee for a week, and the decision proved fateful. The Army of Northern Virginia crossed the Mason-Dixon Line into Pennsylvania, where the Army of the Potomac finally found it at Gettysburg. The armies collided there on July 1 in a battle neither general planned to fight there, and after three days the defeated Confederates retreated, crossing the Potomac River into Virginia on July 14.