More men marched down to the creek where the columns waited for the order to cross. One unit sang “John Brown’s Body” as they marched close to the Pry farm and McClellan scowled. He hated that song and had tried to forbid it being sung. So far as McClellan was concerned there had been nothing to admire in John Brown’s foolish adventure. The man had tried to start a slave rebellion, for God’s sake, and his hanging, McClellan believed, had been richly rewarded. He tried to ignore the music as he stooped to his telescope to watch the troops on the creek’s far side, who were forming up for a new attack on the smoke-wreathed woods. “That’s Mansfield’s corps?” he asked an aide.

“Yes, sir.”

“Tell them to go!”

He would let Mansfield attack and see what happened. At best they would push Lee’s men back and at worst they would provoke the dreaded riposte. McClellan almost prayed for that riposte to happen, for then, at least, the fears would take solid shape and he would know just what he had to deal with. But for now he would go on attacking in the north and stay alert for the horror he knew must come.

Three miles away, in a grove of trees near Sharpsburg, Robert Lee stared at a map. He was not studying the map, indeed he was hardly aware that he was looking at it. Belvedere Delaney was among the aides who hovered nearby. The general liked Delaney and had invited him to keep him company. It was good to have someone slightly irreverent, someone who offered amusement rather than advice.

A crescendo of firing sounded from the higher ground north of the town. In a moment, Lee knew, the gunsmoke would billow above the skyline to mark where the fighting had erupted so suddenly. “That’s it,” he said mildly.

“It?” Delaney asked.

Lee smiled. “Hood’s men, Delaney, almost our last reserves. Not, to be honest, that they were reserves.” Lee had ruthlessly stripped troops from the southern part of his battle line to preserve the army’s northern perimeter so that now, beyond a fragile skin of troops that edged the creek, he had nothing to fight an outflanking attack from the south.

“So what do we do?” Delaney asked.

“Put our trust in McClellan, of course,” Lee said with a smile, “and pray that Ambrose Hill reaches us in time.”

The Light Division was marching as it had never marched before. It was still south of the Potomac and a long way from the ford at Shepherdstown, but the ever-present sound of the big guns was the summons that kept them moving. Staff officers rode up and down the long column urging the men on. Marching troops were usually given ten minutes rest an hour, but not today. Today there could be no rest, just marching. The dust kicked up from the dry road choked men’s throats, some limped on bare bleeding feet, but no one straggled. If a man dropped out he dropped like the dead, dropped out of sheer exhaustion, but most kept grimly going. They had no breath to sing, not even to speak, just to march and march and march. To where the guns were sounding and the piles of dead grew high.