Battle of the Wilderness, battle of the American Civil War, fought on May 5-6, 1864, in a densely thicketed woodland known as the Wilderness, in northeast Virginia. The engagement involved the Army of Northern Virginia, about 62,000 troops under the Confederate general Robert E. Lee, and the Army of the Potomac, about 115,000 troops under the Union general George Gordon Meade. The Union commander in chief, General Ulysses S. Grant, directed Meade's command during the fighting. Determined to sever Lee's lines of communication with Richmond, Virginia, capital of the Confederacy, Grant sent his army across the Rapidan River during the night of May 3, with the intention of moving through the Wilderness into battle positions under cover of darkness. Transport failure kept the Union army in the forest throughout May 4. On the morning of May 5, Lee prepared to attack. Planning to flank the Union line, Lee marched on Grant's forces with two infantry corps, under the Confederate generals Richard Stoddert Ewell and Ambrose Powell Hill. Lee delayed going into action until another infantry corps, under General James Longstreet, could be brought up to support Ewell and Hill. Informed of Lee's preparations, Grant took the initiative and attacked first. Two Union infantry corps opened the battle with an attack against Ewell, and one remained temporarily in reserve; a fourth corps, under the command of General Ambrose Everett Burnside, was located too far north of the battlefield to be brought immediately into action.

Communication difficulties split the battle into disjointed engagements. The terrain precluded effective use of cavalry or artillery. The infantry fighting, much of it hand to hand, was declared by Grant to be the hardest he had ever seen. The forest caught fire, burning many men to death. In the action on May 5, the Confederate forces under Ewell and Hill repulsed Union forces in the morning. In the afternoon the Union reserve corps under General Winfield Scott Hancock launched an attack on Hill's forces, inflicting heavy Confederate losses in a 4-hour fight with the firing lines only about 45 m (50 yd) apart. The Union assault ended, however, without success.

On May 6, Grant renewed the Union drive against Hill, with Hancock attacking again while the other two Union corps blocked Ewell. Hill's defeat appeared certain until Longstreet's corps hurried in and saved the Confederate situation. Burnside, coming to help Hancock with Union reinforcements, arrived too late because of the difficult terrain.

The two-day battle ended at nightfall without decisive outcome. During the night of May 6, General Philip Henry Sheridan, commanding a Union cavalry corps, fought to some advantage against a Confederate cavalry corps of two divisions led by General James Ewell Brown (Jeb) Stuart, but the action was inconsequential. The true significance of the Wilderness lay in what happened after the fighting. Although the Union forces had suffered some 17,500 casualties to the Confederacy's 7000, Grant, instead of retreating, moved south toward Spotsylvania and engaged in another battle there, demonstrating for the first time that his army would be willing to fight every day and suffer tremendous casualties in order to wear down and destroy Lee's army.