The Army of the Potomac pushed stubbornly toward Richmond. Lee tried desperately to block it, winning victories at Spotsylvania (May 12), North Anna (May 23), and Cold Harbor (June 3). In the last-named engagement, over 7,200 Federals fell in less than twenty minutes of fighting. While Lee contested Grant’s moves, another and makeshift Confederate force under Gen. Beauregard repelled a Federal stab (May 15-19) at Richmond and Petersburg by Gen. Benjamin Butler. Grant recognized that he could not take Richmond by direct approach. He shifted his army around the city and moved on Petersburg, a rail junction and important link in the Confederate chain of defenses. Lee at first was unaware of Grant’s plans to attack Petersburg. But Beauregard successfully beat back the initial Federal thrusts, thus forcing Grant to begin what became a nine-month siege of Petersburg. Many probes were made of Lee’s defenses. The most spectacular of these occurred on July 30 and is known as the Battle of the Crater. Coal miners in the 48th Pennsylvania Infantry dug a long tunnel under the Confederate earthworks. Their plan was to explode 8,000 pounds of black powder, blast a mighty gap in the Confederate defenses, and then to use the resulting confusion for a large-scale Federal attack. The explosion and confusion came off as planned. But the Federal assault failed. Grant resumed his tight siege. In the fighting from the Wilderness to Petersburg, the Federal army had suffered 60,000 casualties—more men than were in Lee’s whole army. Yet Grant knew, as did many Confederates, that Lee was now pinned down. The well-equipped and well-fed Federal army could afford to wait. [Illustration: The July 30, 1864, mine explosion, as seen from the Federal lines. Newspaper correspondent Alfred A. Waud made this sketch.] Other related actions took place in Virginia. On May 11, Gen. Philip Sheridan’s cavalry clashed with “Jeb” Stuart’s horsemen a few miles north of Richmond at Yellow Tavern. Sheridan’s men were driven back. Yet this battle cost the Confederacy the colorful Stuart, mortally wounded while leading his troops. On May 15 the Confederates scored another victory in the Shenandoah Valley. Gen. Franz Siegel and 8,000 Federal horsemen advanced up the Valley as far as New Market. There they encountered a hastily assembled Confederate force less than half the size of Siegel’s division. The highlight of the battle was the successful charge of 225 youthful cadets from the Virginia Military Institute. Siegel’s force suffered an embarrassing defeat and fled down the Valley.