'He is…impressive,' Mongke said. 'I am in the right place, I think.'

'Of course you are,' Kachiun said. 'It is incredible, Mongke. Only your grandfather had his touch on campaign. There are times when I think he must be possessed of some warlike spirit. He knows what they will do. Last month, he sent me to the middle of nowhere to wait. I was there just two days when a force came galloping over the hill, three thousand armoured knights riding to relieve Novgorod.' He smiled in memory. 'Where else would you rather be? Safe at home? You were right to come out here. We have one chance to knock the world back on its heels, Mongke. If we can do it, there will be centuries of peace. If not, everything your grandfather built will be ashes in just a generation. Those are the stakes, Mongke. This time, we will not stop until we reach the sea. I swear, if Tsubodai can find a way to put horses on ships, perhaps not even then!' Chagatai rode along the cliffs of Bamiyan with his eldest son, Baidur. North-west of Kabul, the red-brown crags ran outside the lands granted him by Ogedai, but then his family had never truly recognised borders. He grinned at the thought, pleased to be riding in the fading heat, in the shadow of dark peaks. The town of Bamiyan was an ancient place, the houses built of the same dun stone that formed its backdrop. It had suffered conquerors and armies before, but Chagatai had no quarrel with the farmers there. He and his men patrolled areas outside the Amu Darya river, but there was no cause to leave the villages and towns as smoking ruins.

With the khan's shadow stretching over them, they were actually thriving. Thousands of migrant families had come to live in the lands around his khanate, knowing that no one would dare move an army in reach of Samarkand or Kabul. Chagatai had made his authority clear in the first two years, as he took control of an area populated by wild bandits and aggressive local tribes. Most were slaughtered, the rest driven away like goats to take word to those who did not hear. The message had not been lost and many of the townspeople believed that Genghis himself had returned. Chagatai's men had not bothered to correct the error.

Baidur was already tall, with the pale yellow eyes that marked the line from the great khan, ensuring instant obedience among those who had known Genghis. Chagatai watched him closely as he guided his mare across broken ground. It was a different world, Chagatai thought, a little ruefully. At Baidur's age, he had been locked in a struggle with his older brother, Jochi, neither willing to give up the prospect of being khan after their father. It was a bitter-sweet memory. Chagatai would never forget the day when their father had denied them both and made Ogedai his heir.

The air had been baked all day, but as the sun sank, it grew cooler and Chagatai could relax and enjoy the sights and sounds around him. His khanate was a huge area, larger even than the homeland. It had been won by Genghis, but Chagatai would not scorn the gift of his brother. The cliffs were looming closer and he saw Baidur look back at him to see where he wanted to go.

'To the foot of the cliffs,' he said. 'I want you to see a wonder.'

Baidur smiled and Chagatai felt a burst of affection and pride. Had his own father ever felt such an emotion? He did not know. For a moment, he almost wished Jochi alive so he could tell him how different things were, how his world had grown larger than the small inheritance they had fought over. The horizons were wide enough for them all, he realised now, but the wisdom of age is bitter when those you have failed have gone. He could not bring back the years of his youth and live them with greater understanding. How impatient he had been once, how foolish! He had vowed many times not to make the same mistakes with his own sons, but they too would have to find their path. He thought then of another son of his, killed in a raid by some ragged tribesmen. It had just been his bad luck that he had come across them as they camped. Chagatai had made them suffer for the death of that boy. His grief swelled and vanished just as quickly. There had always been death in his life. Yet somehow Chagatai survived where other, perhaps better, men had fallen. His was a lucky line.

At the base of the cliffs, Chagatai could see hundreds of dark spots. From his previous trips, he knew they were caves, some natural, but most hewn from the rock by those who preferred the cool refuges to a brick-built house on the plain. The brigand he sought that day had his base in those caves. Some of them went back into the earth for a great distance, but Chagatai did not think it would be too hard a task. The tuman that rode at his back had brought enough firewood to bank at the entrance to every cave, smoking them out like wild bees from their nest.

In among the dark fingernail smudges of the cave mouths, two fingers of shadow rose above them, immense alcoves cut into the rock. Baidur's sharp eyes picked them out from a mile away and he pointed excitedly, looking to his father for an answer. Chagatai smiled at him in response and shrugged, though he knew very well what they were. It was one reason he had brought his son out on the raid. The dark shapes grew before them as they came closer, until Baidur reined in his mare at the foot of the largest of the pair. The young man was awestruck as his eyes made out the shape inside the cliff.

It was a huge statue, larger than any man-made thing Baidur had ever seen before. The drapes of robes could be seen cut into the brown stone. One hand was held up with an open palm, the other outstretched as if in offering. Its partner was only slightly smaller: two smiling figures looking out onto the fading sun.

'Who made them?' Baidur asked in wonder. He would have walked even closer, but Chagatai clicked his tongue to stop him. The cave-dwellers were sharp-sighted and good with a bow. It would not do to tempt them with his son.

'They are statues of the Buddha, some deity of the Chin,' he said.

'Out here? The Chin are far away,' Baidur responded. His hands opened and closed as he stood there, obviously wanting to walk up and touch the enormous figures.

'The beliefs of men know no borders, my son,' Chagatai said. 'There are Christians and Moslems in Karakorum, after all. The khan's own chancellor is one of these Buddhists.'

'I cannot see how statues could be moved…no, they were cut here, the rock removed around them,' Baidur said.

Chagatai nodded, pleased at his son's sharp wits. The statues had been chiselled out of the mountains themselves, revealed with painstaking labour.

'According to the local men, they have stood here as long as anyone can remember. Perhaps even for thousands of years. There is another one in the hills, a huge figure of a man lying down.'

Chagatai felt an odd pride, as if he were somehow responsible for them himself. His son's simple pleasure was a joy to him.

'Why did you want me to see them?' Baidur asked. 'I am grateful – they are…astonishing – but why have you shown them to me?'

Chagatai stroked the soft muzzle of his mare, gathering his thoughts.

'Because my father did not believe in building a future,' he said. 'He used to say there was no better way for a man to spend his life than in war with his enemies. The spoils and land and gold you have seen came almost by accident from those beliefs. He never sought them for themselves. Yet here is proof, Baidur. What we build can last and be remembered, perhaps for a thousand generations to come.'

'I understand,' Baidur said softly.

Chagatai nodded. 'Today, we will smoke out the thieves and brigands who inhabit the caves. I could have hammered the cliffs with catapults. In months or years, I could have reduced them to rubble, but I chose not to because of those statues. They remind me that what we make can survive us.'