All the planning and preparation was done, and on May 4, 1864 Grant headed the Army of the Potomac south. He had approximately 120,000 men to Lee’s 65,000. Crossing the Rapidan , Grant wanted his army to march quickly through the Wilderness, an almost unsettled area of 70 square miles of dense shrubs and second growth trees where Hooker had come to grief at Chancellorsville just a year before. If Grant could move the Army of the Potomac fast enough through this, he would have turned Lee’s right and could then bring the Army of Northern Virginia to battle in the open country south of the Wilderness where Union numerical superiority would have maximum effect. However, as the Army tramped through the Wilderness where visibility was nil a few yards from the roads and trails, Grant agreed with Meade that the Army would camp in the Wilderness at the conclusion of the day’s march to allow the supply train to catch up. Grant assumed that Lee would be too far away to launch an attack in the Wilderness on the 5th, and one day more was all that Grant needed to be clear of the Wilderness.
Unfortunately for Grant, few generals in American history have had as keen an ability to ferret out an adversaries’ plan as Robert E. Lee. Lee guessed that Grant would cross the Rapidan and march through the Wilderness. He grasped immediately that the salvation of his outnumbered army was to fight in the Wilderness. Ordering Hill and Ewell’s corps to approach and attack from the west, he summoned Longstreet’s corps from Gordonsville, estimating that it would be in position to attack Grant’s left flank on May 6, after a day spent by Hill and Ewell pinning Grant’s army with attacks from the west. The stage was set for the opening great battle of the Overland Campaign.