Barchuk pointed to the ground, jabbing his hand and raising his voice over the unremitting wind. "Do you see the blue flecks in the sand, lord?"

Genghis nodded, his mouth too dry to speak.

"They mark the beginning of the last stage before the Yinshan Mountains. There is copper here. We have traded it with the Xi Xia."

"How much further then before we see these mountains?" Genghis asked hoarsely, refusing to let his hopes rise.

Barchuk shrugged with Mongol impassivity. "We have no certain knowledge, but merchants from Xi Xia are still fresh when they cross our trails in this place, their horses barely marked with dust. It cannot be far now."

Genghis looked back over his shoulder at the silent mass of riders and carts. He had brought sixty thousand warriors into the desert, as many again of their wives and children. He could not see the end of the tail that stretched back for miles, the forms blurring into one another until they were no more than a dark smear wavering in the heat.

The water was almost gone and soon they would have to slaughter the herds, taking only what meat they could carry and leaving the rest on the sands. Barchuk followed his gaze and chuckled.

"They have suffered, lord, but it will not be long now before we are knocking at the doors of the Xi Xia kingdom."

Genghis snorted wearily to himself. The Uighur khan's knowledge had brought them into this bleak place, but they still had only his word that the kingdom was as rich and fertile as he said. No warriors of the Uighur had been allowed to travel beyond the mountains that bordered the desert to the south, and Genghis had no way to plan his attack. He considered this irritably as his horse sent another scorpion skittering over the sand. He had staked them all on the chance at a weak point in the Chin defenses, but he still wondered what it would be like to see a great city of stone, as tall as a mountain. Against such a thing, his horsemen might only stare in frustration.

The sand under his pony's hooves grew blue-green as they rode, great stripes of the strange colors stretching away in all directions. When they stopped to eat, the children threw it into the air and drew pictures with sticks. Genghis could not share their pleasure, as the supply of water dwindled and each night was spent shivering despite the hot rocks.

There was little to amuse the army before they fell into weary sleep. Twice in twelve days, Genghis had been called to settle some dispute between tribes as heat and thirst made tempers flare. Both times, he had executed the men involved and made it clear that he would not allow anything to threaten the peace of the camp. He considered them to have entered enemy lands, and if the officers could not handle a disturbance, his involvement meant a ruthless outcome. The threat was enough to keep most of the hotheaded warriors from outright disobedience, but his people had never been easy to rule and too many hours in silence made them fractious and difficult.

As the fourteenth dawn brought the great heat once more, Genghis could only wince as he threw off his blankets and scattered the stones under him to be collected for the next night by his servants. He felt stiff and tired, with a film of grit on his skin that made him itch. When little Jochi stumbled into him in some game with his brothers, Genghis cuffed him hard, sending him weeping to his mother for solace. They were all short-tempered in the desert heat, and only Barchuk's promises of a green plain and a river at the end kept their eyes on the horizon, reaching out to it in imagination.

On the sixteenth day, a low rise of black hills appeared. The Uighur warriors riding as scouts came back at a canter, their mounts sending up puffs of sand and laboring through its grip. Around them, the land was almost green with copper, and black rocks poked through like sharp blades. Once more the families could see lichen and scrub bushes clinging to life in the shadow of the rocks, and at dawn the hunters brought hares and voles caught in their night traps. The mood of the families lifted subtly, but they were all suffering from thirst and sore eyes, so that tempers remained foul in the camp. Despite their tiredness, Genghis increased the patrols around the main force and had the men drill and practice with their bows and swords. The warriors were dark and whip-thin from the desert, but they took to the work with grim endurance, each man determined not to fail under the eyes of the great khan. Slowly, imperceptibly, the pace increased once more, while the heavier carts drifted to the rear of the procession.

As they drew closer to the hills, Genghis saw that they were far higher than he had realized. They were made of the same black rock that broke through the sand around him, sharp and steep. Climbing them was impossible and he knew there would have to be a pass through the peaks or he would be forced to travel right around their length. With their water supply almost gone, the carts were lighter, but he knew they had to find Barchuk's valley quickly or they would begin to die. The tribes had accepted him as khan, but if he had brought them to a place of heat and death, if he had killed them, they would take revenge while they still had the strength. Genghis rode straight-backed in the saddle, his mouth a mass of sores. Behind him, the tribes muttered sullenly.

Kachiun and Khasar squinted through the heat-hazed air at the foot of the cliffs. With two of the scouts, they had ridden ahead of the main army to look for a pass. The scouts were experienced men and the sharp eyes of one had pointed out a promising cut between peaks. It started well enough as the steep slopes gave way into a narrow canyon that echoed to the hooves of the four riders. On either side, the rocks extended up toward the sky, too high for a man to climb alone, never mind with carts and horses. It took no special skill in tracking to see the ground had been worn away in a wide path, and the small group kicked their mounts into a canter, expecting to be able to report a way through to the Xi Xia kingdom beyond the hills

As they rode around a kink in the trail, the scouts drew rein in astonishment, awed to silence. The end of the canyon was blocked by a huge wall of the same black stone as the mountains themselves. Each block on its own would have been heavier than anything the tribes could move, and the wall seemed strange, somehow wrong to their eyes. They had no craftsmen who worked in stone. With its neat lines and smooth surfaces, it was clearly the work of man, but the sheer size and scale was something they had only seen in wild rocks and valleys. At the base was the final proof that it was not a natural thing. A gate of black iron and wood was set into the base of the wall, ancient and strong.

"Look at the size of it!" Kachiun said, shaking his head. "How are we going to get through that?"

The scouts merely shrugged and Khasar whistled softly to himself.

"It would be easy to trap us in this spiritless place. Genghis must be told quickly, before he follows us in."

"He'll want to know if there are warriors up there, brother. You know it."

Khasar eyed the steep slopes at either side, suddenly feeling vulnerable. It was easy to imagine men dropping stones from the top, and there would be no way to avoid them. He considered the pair of scouts who had accompanied them into the canyon. They had been warriors of the Kerait before Genghis had claimed them. Now they waited impassively for orders, hiding their awe at the size of the wall ahead.

"Perhaps they just built it to block an army from the desert," Khasar said to his brother. "It might be unmanned."

As he spoke one of the scouts pointed, directing their gaze to a tiny figure moving along the top of the wall. It could only be a soldier and Khasar felt his heart sink. If there was another pass, Barchuk did not know of it, and finding a way past the mountains would see the army of Genghis begin to wither. Khasar made his decision, knowing it could mean the lives of the two scouts.