A. P. Hill's corps did not leave Fredericksburg until the 14th of June, just after Hooker put the Army of the Potomac in motion to the northward. Hill marched into the Valley and joined Longstreet at Berryville, and from there preceded him to Chambersburg, and by one day to Cashtown and Gettysburg.( 5) General J. E. B. Stuart, in command of the Confederate cavalry, crossed the upper Rappahannock, June 16th, and moved east of the Blue Ridge on Longstreet's right flank, leaving only a small body of cavalry on the Rappahannock, in observation, with instructions to follow on the right flank of Hill's corps. Severe cavalry engagements took place at Aldie, the 17th, and at Middleburg, Uppeville, and Snicker's Gap, without decisive results, both sides claiming victories. On the 24th Stuart, with the main body of his cavalry, succeeded in eluding the Union cavalry and Hooker's army (then feeling its way north), and passed east of Centreville, thence _via_ Fairfax Court-House and Dranesville, and crossed, July 27th, the Potomac at Rowser's Ford, and captured a large supply train between Washington and Rockville. Stuart's cavalry caused some damage in the rear and east of the Army of the Potomac, but, on the whole, this bold movement contributed little, if any, towards success in Lee's campaign. Stuart's advance reached the Confederate left _via_ Dover and Carlisle, Pennsylvania, late on the afternoon of the second day of the battle, his troopers and horses in a somewhat exhausted condition. The consensus of opinion among military critics was then, and since is, that Lee committed a great strategic error in authorizing his main cavalry force to be separated from close contact with the right of his moving army. General Lee seems to have come to this conclusion himself, as frequently, in his official reports of the campaign, he deplores the absence of his cavalry and his consequent inability to obtain reliable information of the movements of the Army of the Potomac.( 6) Longstreet severely criticises Stuart's raid, and attributes to the absence of the cavalry, in large part, the failure of the Gettysburg campaign.( 7) Cavalry, under an energetic commander, are the _eyes and ears_ of a large army, especially when it is on an active campaign against a vigilant enemy.