18. Grant again moved to the left, and came to Cold Harbor, twelve miles northeast of Richmond. Here, on the 1st of June, he attacked the Confederates, but was repulsed with heavy losses. On the morning of the 3d the assault was renewed, and in half an hour nearly ten thousand Union soldiers fell dead or wounded before the Confederate intrenchments. The repulse of the Federals was complete, but they held their lines as firmly as ever. 19. General Grant now changed his base to James River. General Butler had already taken City Point and Bermuda Hundred. Here, on the 15th of June, he was joined by General Grant's whole army, and the combined forces moved forward and began the siege of Petersburg. [Sidenote: Operations in the Valley.] 20. Meanwhile important movements were taking place on the Shenandoah. When Grant moved from the Rapidan, General Sigel marched up the valley to New Market, where he was met and defeated by the Confederate cavalry, under General Breckinridge. The latter then returned to Richmond, whereupon the Federals faced about, overtook the Confederates at Piedmont, and gained a signal victory. From this place Generals Hunter and Averill advanced against Lynchburg. By this movement the valley of the Shenandoah was again exposed to invasion. [Illustration: Philip H. Sheridan.] 21. Lee immediately dispatched General Early to cross the Blue Ridge, invade Maryland and threaten Washington City. With twenty thousand men Early began his march, and on the 5th of July crossed the Potomac. On the 9th he defeated the division of General Wallace on the Monocacy. But the battle saved Washington and Baltimore from capture. 22. General Wright followed Early as far as Winchester. But the latter wheeled upon him, and the Union troops were driven across the Potomac. Early next invaded Pennsylvania and burned Chambersburg. General Grant now appointed General Philip H. Sheridan to command the army on the Upper Potomac. The troops placed at his disposal numbered nearly forty thousand. On the 19th of September, Sheridan marched upon Early at Winchester, and routed him in a hard-fought battle. On the 22d of September he gained another complete victory at Fisher's Hill. [Sidenote: =Sheridan's Ride from Winchester.=]