'I have no horse, my lord,' Batu said.

Ogedai glanced at the warrior who had struck him and the man raised his eyes to heaven before dismounting. He passed the reins into Batu's hands.

'Can you ride at least?' the warrior said.

Batu was awed as he took the reins and patted the muscular neck. He had never touched an animal as fine.

'Yes. Yes, I can ride.'

'Good. This mare is not your horse, understand? She will carry you to your post, but then you will take some old sway-back and return her to me.'

'I don't know your name,' Batu said.

'Alkhun, boy. Ask anyone in Karakorum and they'll know me.'

'The city?' Batu asked. He had heard of the stone thing rising from the soil on the back of a million workers, but until then, he had not believed it.

'More a camp than a city at the moment, though that is changing,' Alkhun confirmed. 'You can send the horse by the way station riders, but tell them to go easy with her. I'll take any whip marks out of your hide. Oh, and welcome to the army, boy. My lord Ogedai has plans for you. Don't disappoint him.'

The air swirled with marble dust that glittered as it caught the evening sun. Ogedai's heart was full as he guided his horse down the main thoroughfare, taking in every sight and sound around him. There was a sense of urgency in the cacophony of hammer blows and shouted orders. The Mongol tumans had gathered outside the city. His generals, his people had been summoned there to see what two years of labour had created: a city in a wilderness, with the Orkhon river tamed and bent to his will.

Ogedai reined in for a moment to watch a group of workmen unload a cart. Nervous under his gaze, the labourers used ropes, pulleys and sheer numbers to manoeuvre blocks of white marble onto low sledges that could be dragged into the workshops. Each milky block was subtly veined in a light blue that pleased Ogedai. He owned the quarry that had birthed the stones, hundreds of miles to the east, just one of a thousand purchases he had made in the last years.

There was no doubt he had been extravagant, spending gold and silver as if it had no value. He smiled at the thought, wondering what his father would have made of the white city rising in the wilderness. Genghis had despised the anthills of humanity, but these were not the ancient stones and teeming streets of an enemy. This was new and it belonged to the nation.

There had never been a treasury like the one he had inherited, amassed from the wealth of China and Khwarezm, yet never spent by its khan. With the tribute from Yenking alone, Ogedai could have sheathed every new home in white marble or even jade if he had wanted. He had built a monument to his father on the plains, as well as a place where he himself could be khan. He had built a palace with a tower that rose above the city like a white sword, so that all men could see the nation had come far from simple gers and herds.

For his gold, a million men had come to work. They had crossed plains and deserts with just a few animals and tools, coming from as far off as Chin lands or the cities of Samarkand, Bukhara and Kabul. Masons and carpenters from Koryo had made the journey, called to the west by rumours of a new city being built on a river of coins. Bulgars brought stocks of rare clays, charcoal and hardwood in great caravans from their forests. The city filled with traders, builders, potters, foodsellers, thieves and scoundrels. Farmers scenting a profit brought their carts for days of travel, all for the strings of metal coins. Ogedai gave them gold and silver from the earth, melted and shaped. In return, they gave him a city, and he did not find it a bad bargain. For the present, they were the colourful crowds of his city, speaking a hundred tongues and cooking a thousand different foods and spices. Some of them would be allowed to stay, but he was not building it for them.

Ogedai saw green-handed dyers flatten themselves against the walls, their red turbans dipping in respect. His Guards cleared the way ahead, so the son of Genghis could ride almost in a dream. He had made this place from the camp of gers his father had known. He had made it real, in stone.

It still amazed him. He had not paid for women to travel with his workers, but they had come with their husbands and fathers. He had wondered for a time how he would establish the businesses every city needed to thrive, but traders had approached his chancellor, offering horses or more silver to lease new properties. The city was more than a simple collection of houses. Already it had a vitality of its own, far beyond his control.

Yet not completely. A quirk in the plans had created an area of small alleyways in the south of his city. Criminal gangs had begun to flourish there until Ogedai heard. He had ordered eight hundred buildings torn down, the whole area redesigned and rebuilt. His own Guard had supervised the hangings.

The street fell quiet as he passed, the labourers and their masters bowing their heads as they saw the man who held the power of life and death and gold over all of them. Ogedai took a deep breath of the dusty air, enjoying the taste of it on his tongue and the thought that he was literally breathing in his creation. Ahead, he could see the towers of his palace, crowned in a dome of gold beaten thinner than the paper of his scribes. It raised his spirits to see it, like sunlight trapped and held in his city.

The street widened as it grew before him, its stone gutters polished. That section had been finished months before and the bustling crowds of labourers fell behind. As Ogedai trotted on, he could not help glancing at the boundary walls that had so confused his Chin architects and labourers. Even from the low vantage point of a saddle, there were moments when he could see over them to the green plains beyond. The walls of Yenking had not saved that city from fire or siege, he knew. His walls were the warriors of the khan, the tribes who had brought a Chin emperor to his knees and razed a shah's cities.

Already, Ogedai loved his creation, from the vast expanse of the central training ground, to the red-tiled roofs, the paved gutters, the temples and churches and mosques and markets and homes by the thousand, most still empty and waiting for life. Scraps of blue cloth fluttered in the plains wind on every corner, a tribute to the sky father above them all. In the south, green foothills and mountains stretched far away and the air was warm with dust as Ogedai rejoiced in Karakorum.

The twilight was deepening into a soft gloom as Ogedai handed his reins to a servant and strode up the steps to his palace. Before he entered, he looked back once more at the city straining to be born. He could smell fresh-turned earth and, over it, the fried food of the workmen on the evening air. He had not planned the herds of livestock in corrals beyond the walls, or the squawking chickens sold on every corner. He thought of the wool market that had sprung up by the western gate. He should not have expected trade to halt simply because the city was unfinished. He had chosen a spot on an ancient traders' road to give it life – and life had begun pouring in while whole streets, whole districts, were still piles of lumber, tile and stone.

As he looked into the setting sun, he smiled at the cooking fires on the plains surrounding the city. His people waited there, for him. His armies would be fed on rich mutton, dripping fat from the summer grass. It reminded him of his own hunger and he moistened his lips as he passed through a stone gate the equal of anything in a Chin city.

In the echoing hall beyond, he paused for a moment at his most extravagant gesture. A tree of solid silver stretched gracefully up to the arched ceiling, the centre point open to the sky like the ger of any herdsman. It had taken the silversmiths of Samarkand almost a year to cast and polish, but it served his purpose. Whoever entered his palace would see it and be staggered at the wealth it represented. Some would see an emblem for the silver people, the Mongol tribes who had become a nation. Those with more wisdom would see that the Mongols cared so little for silver that they used it as a casting metal.