In the spring of 1864, Virginia remained unbroken, its armies having repelled Northern armies for more than two years. Robert E. Lee's Army of Northern Virginia had defeated the campaigns of four Union generals, and Lee's veterans were confident they could crush the Union offensive this spring, too. But their adversary in 1864 was a different kind of Union commander-Ulysses S. Grant. The new Union general-in-chief had never lost a major battle while leading armies in the West. A quiet, rumpled man of simple tastes and a bulldog's determination, Grant would lead the Army of the Potomac in its quest to destroy Lee's army. During six weeks in May and June 1864, Grant's army campaigned as no Union army ever had. During nearly continual combat operations, the Army of the Potomac battered its way through Virginia, skirting Richmond and crossing the James River on one of the longest pontoon bridges ever built. No campaign in North American history was as bloody as the Overland Campaign. When it ended outside Petersburg, more than 100,000 men had been killed, wounded, or captured on battlefields in the Wilderness, near Spotsylvania Court House, and at Cold Harbor. Although Grant's casualties were nearly twice Lee's, the Union could replace its losses. The Confederacy could not.