Genghis squinted ahead as the prisoners streamed under the forts. The pass was crammed with men so far ahead of his own people that he could barely see what was happening. In the distance, he heard screams come back on the frozen air and saw a sudden bloom of flame. The prisoners at the rear had seen it too and they faltered in the mad rush before his riders, terrified. Without an order from him, lances came down and forced them onward into the maw between the forts. No matter what weapons the Chin had, thirty thousand prisoners were hard to stop. Already some of them were past the pinch and streaming out beyond it. Genghis rode on and could only hope that by the time he came under the forts, they would have exhausted their oil and shafts. Bodies lay still on the ground, more and more of them as he closed on the narrow place.

Above his head, Genghis saw archers on the forts, but to his astonishment, they seemed to be aiming across the pass itself, loosing shaft after shaft at their own men. He could not understand it and a spike of worry came into his thoughts at the development. Though it seemed a gift, he did not like to be surprised when he was hemmed into such a place. He felt the walls of rock pressing on him, forcing him on.

Closer to the forts he could hear the thump of catapults, now a sound he knew well and understood. He saw a smoke trail crease the air above the pass and a wash of fire spread over the walls of the fort on his left hand. Archers fell burning from their platforms and a cheer went up from the other side. Genghis felt his heart leap. There could only be one explanation and he roared orders to thin the column so that it passed on the right side of the Badger's Mouth, as far from the left as they could manage.

Kachiun or Khasar had taken the fort. Whoever it was up there, Genghis would honor him when the battle was over, if they both still lived.

More and more corpses lay sprawled on the floor of the pass, so that his horse had to step on them, whinnying in distress. Genghis felt his heart hammer in fear as a bar of shadow crossed his face. He was almost under the forts, in the heart of a killing ground designed by long-dead Chin nobles. Thousands of his prisoners had died and there were places he could hardly see the ground for bodies. Yet his ragged vanguard had pushed through, running now in wild terror. The Mongol tribes themselves had hardly lost a man, and Genghis exulted. He passed under the right-hand fort, shouting loudly to those of his people above who had smashed their way in. They could not hear him. He could hardly hear himself.

He leaned forward in the saddle, needing to gallop. It was difficult to hold his mount to a trot with arrows in the air, yet he controlled himself, holding up a flat palm to keep the men steady. One of the forts was burning inside, the flames licking out of the killing holes. Even as Genghis glanced up, a wooden platform collapsed in fire, tumbling to the ground below. Horses screamed in distress and some of them bolted, racing after the prisoners.

Genghis stood in the saddle to look down the pass. He swallowed nervously as he saw a dark line across its end. There the pass was as narrow as the pinch between the forts, a perfect natural defense. There was no way through but over the army of the Chin emperor. Already the prisoners were reaching it and now Genghis heard the snap of crossbow volleys like thunder, so loud in the confined space that it hurt his ears with every strike.

The prisoners went berserk in their panic, bolts hammering them from their feet as each man was struck over and over, spinning and torn as he fell. They ran into a hailstorm of iron and Genghis bared his teeth, knowing his turn would come.

The general's messenger was pale with fear, still shaking at what he had seen. Nothing in his career to that point had prepared him for the carnage of the pass.

"They have taken one of the forts, General," he said, "and turned the catapults on the other."

General Zhi Zhong looked calmly at the man, irritated with his show of fear. "The forts could only have thinned so many," he reminded the man. "We will stop them here. "

The messenger seemed to take confidence from the general's composed manner and let out a long breath.

Zhi Zhong waited for the messenger to control himself, then gestured to one of the soldiers nearby. "Take this one out and whip the skin from his back," he said. The messenger gaped at hearing the order. "When he has learned courage, you may cease the instruction, or at sixty strokes of the cane, whichever comes first."

The messenger bowed his head in shame as he was led away, and for the first time that morning, Zhi Zhong was left alone. He swore under his breath for a moment before striding outside his tent, hungry for information. He knew by then that the Mongols were driving Chin prisoners before them, soaking up the defenses with his own people. Zhi Zhong could silently applaud the tactic, even as he sought ways to counter it. Tens of thousands of unarmed men could be as dangerous as an army if they reached his lines. They would foul the crossbow regiments he had spread across the pass. He ordered a waiting soldier to send fresh carts of bolts to the front and watched as they trundled away.

The khan had been clever, but the prisoners would only be a shield until they were dead and Zhi Zhong was still confident. The Mongols would have to fight for every foot. Without space to maneuver, they would be drawn in and slaughtered.

He waited, wondering if he should move closer to the front line. From his viewpoint further back, he could see black smoke rising from the captured fort and cursed again. It was a humiliating loss, but the emperor would not care once the last of the tribesmen were dead.

Zhi Zhong had hoped to kill many of them before opening a path into his army, compressing them further. They would race forward into the gap and find themselves attacked on all sides, the spearhead lost in a mass of veteran soldiers. It was a good tactic. The alternative was to block the pass completely. He had planned for both and he weighed one against the other. He calmed his racing heart, showing a confident expression to the men around him. With a steady hand, he took a jug of water and poured it into a cup, sipping as he stared down the pass.

Out of the corner of his eye, he saw movement in the snow-covered valley. He glanced over and froze for a moment. Dark lines of men were spilling out of the treeline, forming ranks as he watched.

Zhi Zhong threw the cup down as messengers raced through the camp to tell him of the development. The peaks could not be climbed. It was impossible. Even in his shock, he did not hesitate, snapping orders before the messengers could reach him.

"Cavalry regiments one to twenty, form up!" he roared. "Hold the left flank and sweep those lines away." Horsemen raced to pass on the orders and half his cavalry force began to peel off the main army. He watched the Mongol lines form, striding through the snow toward him. He did not allow himself to panic. They had climbed the peaks on foot and they would be exhausted. His men would ride them down.

It seemed to take an age for twenty thousand Imperial riders to form in blocks on the left flank, and by that point, the Mongol lines had halted. Zhi Zhong clenched his fists as orders sounded up and down the line and his horsemen began to trot toward the enemy, standing in the snow. He could see no more than ten thousand of them, at most. Infantry could not stand against a disciplined charge. They would be destroyed.

As the general watched, his cavalry accelerated, swords raised to take heads. He forced himself to look back at the pass, his mouth dry. They had driven prisoners before them, taken one of his forts, and flanked him over the peaks. If that was all they had, he could still break them. For an instant, his certainty wavered and he considered ordering the pass blocked. No, it had not yet come to that. His respect for the Mongol khan had increased sharply, but the general remained confident as his cavalry thundered down the valley.