The fight for the Sunken Road had exhausted both sides. At 1 p.m. they halted, and panting men grabbed their canteens to swish the dust and powder from their rasping throats.
The Confederate retreat from Bloody Lane had uncovered a great gap in the center of Lee’s line. A final plunge through this hole would sever the Confederate army into two parts that could be destroyed in detail. “Only a few scattered handfuls of Harvey Hill’s division were left,” wrote Gen. William Allen, “and R. H. Anderson’s was hopelessly confused and broken.... There was no body of Confederate infantry in this part of the field that could have resisted a serious advance.” So desperate was the situation that General Longstreet himself held horses for his staff while they served two cannon supporting Hill’s thin line.
But McClellan’s caution stopped the breakthrough before it was born. Though Franklin’s VI Corps was massed for attack, McClellan restrained it. “It would not be prudent to make the attack,” he told Franklin after a brief examination of the situation, “our position on the right being ... considerably in advance of what it had been in the morning.”
So McClellan turned to defensive measures. Franklin’s reserve corps would not be committed, but would remain in support of the Federal right. And in the center, McClellan held back Fitz-John Porter’s V Corps. After all, reasoned the Federal commander, was not this the only force that stood between the enemy and the Federal supply train on the Boonsboro Pike?
But Porter was not quite alone. The entire Federal artillery reserve stood with him. Further, Brig. Gen. Alfred Pleasonton had placed his cavalry and artillery on a commanding ridge west of the Middle Bridge during the morning. From here he had already supported the attack by Sumner’s corps on the Sunken Road, and he had aided Burnside’s efforts on the left. Now he stood poised for further action. Pleasonton was to wait in vain. His dual purpose of obtaining “... an enfilading fire upon the enemy in front of Burnside, and of enabling Sumner to advance to Sharpsburg” was nullified by McClellan’s decision to halt and take the defensive.
In striking contrast to McClellan’s caution, General Lee was at that very moment considering a complete envelopment of the Federal flank at the North and East Woods. By this means he might relieve the pressure on D. H. Hill; for despite the lull, Lee could not believe that McClellan had halted the attack there. If the attack in the North Woods succeeded, Lee hoped to drive the Federal remnants to the banks of Antietam Creek and administer a crushing defeat.
Jackson and J. E. B. Stuart, early in the afternoon, shifted northward and prepared to charge the Federal lines. When they arrived close to the powerful Federal artillery on Poffenberger Ridge, they saw that a Confederate attack there would be shattered by these massed guns. A wholesome respect for Federal artillerists now forced Lee to withdraw his order. As he did so, heavy firing to the south heralded a new threat developing there.
Burnside Takes the Lower Bridge
During the morning of the 17th, Confederate observers on the ridge north of Sharpsburg had spotted masses of Federals moving southward beyond Antietam Creek. These were the four divisions of Burnside’s IX Corps concentrating for the attack on the Lower Bridge.
Topography at the Lower Bridge heavily favored the few hundred Georgia men who defended it under the leadership of Brig. Gen. Robert Toombs. The road approaching the east end of the bridge swings on a course paralleling that of Antietam Creek; in the last few hundred yards before reaching the bridge, the road plunges into a funnel-like depression between the opposing bluffs of the creek. Toombs’ men were in rifle pits on the west bluff overlooking the bridge and the approach road.