In several ways, Marye's Heights offered the Federals their most promising target. Not only did this sector of Lee's defenses lie closest to the shelter of Fredericksburg, but the ground rose less steeply here than on the surrounding hills.
Nevertheless, Union soldiers had to leave the city, descend into a valley bisected by a water-filled canal ditch, and ascend an open slope of 400 yards to reach the base of the heights. Artillery atop Marye's Heights and nearby elevations would thoroughly blanket the Federal approach. "A chicken could not live on that field when we open on it," boasted on Confederate cannoneer.
Sumner's first assault began at noon and set the pattern for a ghastly series of attacks that continued, one after another, until dark. As soon as the Northerners marched out of Fredericksburg, Longstreet's artillery wreaked havoc on the crisp blue formations. The Unionists then encountered a deadly bottleneck at the canal ditch which was spanned by partially-destroyed bridges at only three places. Once across this obstacle, the attackers established shallow battle lines under cover of a slight bluff that shielded them from Rebel eyes.
Orders then rang out for the final advance. The landscape beyond the canal ditch contained a few buildings and fences, but from the military perspective it provided virtually no protection. Dozens of Southern cannon immediately reopened on the easy targets, and when the Federals traversed about half the remaining distance, sheets of flame spewed forth from the Sunken Road. This rifle fire decimated the Northerners. Survivors found refuge behind a small swale in the ground or retreated back to the canal ditch valley.
Quickly a new Federal brigade burst toward Marye's Heights and the "terrible stone wall," then another, and another, until three entire divisions had hurled themselves at the Confederate bastion. In one hour, the Army of the Potomac lost nearly 3,000 men; but the madness continued.
Although General Cobb suffered a mortal wound early in the action, the Southern line remained firm. Kershaw's Brigade joined North Carolinians in reinforcing Cobb's men in the Sunken Road. The Confederates stood four ranks deep, maintaining a ceaseless line of fire while the gray-clad artillerists fired over their heads.More Union units tested the impossible. "We came forward as though breasting a storm of rain and sleet, our faces and bodies being only half- turned to the storm, our shoulders shrugged," remembered one Federal. "Everybody from the smallest drummer boy on up seemed to be shouting to the full extent of his capacity," recalled another. But each blue wave crested short of the goal. Not a single Union soldier laid his hand on the stone wall.