realized—that he would be forced into a siege in defense of the Confederate capital. Petersburg, a prosperous city of 18,000, was a supply center for Richmond, given its strategic location just south of the capital, its site on the Appomattox River that provided navigable access to the James River, and its role as a major crossroads and junction for five railroads. Since Petersburg was the main supply base and rail depot for the entire region, including Richmond, the taking of Petersburg by Union forces would make it impossible for Lee to continue defending the Confederate capital. This represented a change of strategy from that of Grant's Overland Campaign, in which confronting and defeating Lee's army in the open was the primary goal. Now, Grant selected a geographic and political target and knew that his superior resources could besiege Lee there, pin him down, and either starve him into submission or lure him out for a decisive battle. Lee at first believed that Grant's main target was Richmond and devoted only minimal troops under Gen. P.G.T. Beauregard to the defense of Petersburg as the siege of Petersburg began. The Overland Campaign was a thrust necessary for the Union to win the war, and although Grant suffered a number of setbacks, the campaign turned into a strategic success for the Union. By engaging Lee's forces and not permitting them to escape, Grant forced Lee into an untenable position. But this came at a high cost. The campaign was the bloodiest in American history: approximately 55,000 casualties on the Union side (of which 7,600 were killed), 33,600 (4,300 killed) on the Confederate. Lee's losses, although lower in absolute numbers, were higher in percentage (over 50%) than Grant's (about 45%), and more critically, while Grant could expect reinforcements to replace his army's losses, Lee largely could not. His losses were irreplaceable. Furthermore, the public interprets the results of the campaign based on these casualty lists. Dr. Earl Hess states, "The observer should not be fooled by the gory assaults that riveted everyone's attention from Spotsylvania onward—the Overland Campaign was at its heart a campaign of maneuver...Grant's most significant achievement in the Overland Campaign was not capturing territory or reducing the fighting of strength of the Army of Northern Virginia by 50%; rather, it lay in robbing Lee of the opportunity to launch large scale offensives against the Army of the Potomac." Estimates vary as