General Burnside formed his troops on the farm of Mr. Rohrbach, with Sturgis's division on the right, Wilcox in the center, Rodman on the left, and Cox's division, commanded by Crook, in reserve. Benjamin's battery of twenty-pounder Parrotts, Simmons's, McMullen's, Durrell's, Clark's, Muhlenburgh's, and Cook's batteries were stationed on the hills and knolls of Rohrbach's estate during the night of the 16th. The troops lay on their arms, prepared to move whenever General McClellan issued the order. At daybreak the Rebel batteries on the Sharpsburg hills began a rapid fire. The shells fell among the troops. Here and there a man was struck down, but they maintained their ground with great endurance. It was a severe test to the new regiments, which never had been under fire. It requires strong nerves to lie passive, hour after hour, exposed to a cannonade. But the men soon learned to be indifferent to the screaming of the something unseen in the air. They ate their hard tack, and watched the distant flashes from the white cloud upon the Sharpsburg hills. They talked of the guns, and learned to distinguish them by the sound. "That is a rifle shot." "There comes a shell." "I wonder where that will strike." With such remarks they whiled away the moments. The Rebel brigade holding the bridge was commanded by General Toombs. Before the arrival of A. P. Hill, the force of the enemy on this part of the field was about six thousand. So vigorous was Burnside's attack, that nothing but the arrival of Hill prevented an irretrievable defeat.[70] [Footnote 70: Charleston Courier's account of the battle.] Burnside received his orders at ten o'clock.[71] Hooker had been at it all the morning. Standing by his head-quarters, Burnside could see the dark lines moving to and fro on Miller's field. Mansfield was going up the slope. Sumner was crossing the Antietam. The batteries all along the line were thundering. [Footnote 71: Burnside's Testimony.] "You are to carry the bridge, gain the heights beyond, and advance along their crest to Sharpsburg, and reach the rear of the enemy," was the order from General McClellan to General Burnside. Easily ordered; not so easily accomplished. Burnside has less than fourteen thousand men to accomplish a task harder than that assigned to any other commander. He must carry the bridge, gain the ridge, then move over an open field to attack the heights beyond, which are steeper and more easily defended than the ledges by the church, or the hills west of the sunken road. It is by nature the strongest part of the line. Burnside's batteries opened with renewed vigor. Cox, commanding the corps (Burnside commanding the left wing), detailed Colonel Kingsbury with the Eleventh Connecticut to act as skirmishers, and drive the Rebel sharpshooters from the head of the bridge.