'It is important to choose the ground, then scout it well for hidden obstacles,' Tsubodai replied.

Batu chuckled and stared down again. For all his bluster and arrogance, Tsubodai saw he was taking in every detail of the land, his eyes flickering back and forth as he memorised it. He was an unpleasant student, but his mind was as sharp as anyone Tsubodai had known. It was hard not to think of his father at times, the memories robbing the general of his irritation.

'Tell me what you see in our tumans,' Tsubodai went on.

Batu shrugged. Down below, he could see five columns moving slowly across the land. It took just a glance for him to read them.

'We march apart and attack together. Five fingers covering as much ground as possible. The messengers keep them in contact for quick response to any show of force. I believe my grandfather began the practice. It has worked well enough since then.'

He grinned without looking at Tsubodai. Batu knew the general was responsible for the formation that allowed a small army to sweep across huge areas, clearing towns and villages before them so that they left a smoking landscape behind. They came together only when the enemy appeared in strength, when the arrow messengers would bring the tumans racing, a fist to smash the resistance before they moved on.

'Your eyes are strong, Batu. Tell me what else you see.'

Tsubodai's voice was maddeningly calm and Batu rose to the bait, determined to show the older man that he needed no lessons from him. He spoke quickly and used his hand to chop the air.

'For each column, there are scouts at the front in groups of ten. They ride up to eighty miles out, looking for the enemy. The centre is the families, the baggage, gers, oxen, camels, drummers and collapsed gers by the thousand. There are mobile forges on carts with spoked wheels, iron-reinforced. I believe you are responsible for those, general. Boys and foot warriors march there, our final defence if the warriors are ever overrun. Around them are the herds of sheep, goats and of course remounts, three to a man or more.' He spoke faster, enjoying the chance to show his knowledge: 'Beyond those are the heavy tuman cavalry in minghaan ranks. Further still, we have the light cavalry screen, the first to meet any attack with arrows. Finally, we have the rearguard, who plod along and wish they were closer to the front instead of riding through everyone else's shit. Shall I begin naming the officers? You are the orlok, in overall command, I am told. You have no bloodline worth mentioning, so I am the prince whose name appears on the orders, the grandson of Genghis Khan. It is an odd arrangement, but we will discuss it another time. I lead a tuman, as do generals Kachiun, Jebe, Chulgetei and Guyuk. The minghaan officers, in order of seniority are…'

'That is enough, Batu,' Tsubodai said quietly.

'Ilugei, Muqali, Degei, Tolon, Onggur, Boroqul…'

'Enough,' Tsubodai snapped. 'I know their names.'

'I see,' Batu said, raising an eyebrow. 'Then I do not understand what you wanted me to learn by losing half a day riding up this rock with you. If I have made mistakes, you must feel able to bring them to me. Am I in error, general? Have I displeased you in some way? You must tell me, so I can remove the fault.'

His eyes bored into Tsubodai, allowing his bitterness to show for once. Tsubodai controlled his temper, felt it rise in him and took a firmer grip before he ruined a young man guilty of nothing more than spite and arrogance. He looked too much like Jochi for Tsubodai not to know he had reason.

'You have not mentioned the auxiliaries,' Tsubodai said calmly, at last. In response, Batu chuckled, an unpleasant sound.

'No, and I will not. Our ragged conscripts are good for nothing more than soaking up the missiles of our enemies. I am going to rejoin my tuman, general.'

He began to turn his mount and Tsubodai reached out and took his reins. Batu glared at him, but he had the sense not to reach for the sword that hung at his waist.

'I have not yet given you permission to leave,' Tsubodai said.

His face was still emotionless, but his voice had hardened and his eyes were very cold. Batu smiled and Tsubodai could see he was on the point of saying something that would tear down the strained courtesy between them. This was why he preferred to deal with more senior men, who had some idea of consequences and would not throw their entire lives away on a bad-tempered moment. Tsubodai spoke quickly and firmly to head him off.

'If I have the slightest doubt about your ability to follow my orders, Batu, I will send you back to Karakorum.' Batu began to take a breath, his face twisting as Tsubodai went on relentlessly. 'You may take your complaints to your uncle there, but you will no longer ride with me. If I give you a hill to take, you will destroy your entire tuman rather than fail. If I tell you to ride to a position, you will break your horses to reach it in time. Do you understand? If you fail me in anything, there will be no second chance. This is not a game, general, and I do not care what you think of me, not at all. Now, if you have something to say to me, say it.'

At almost twenty, Batu had matured in the years since winning the horse race at Karakorum. He took command of his temper with a swiftness that surprised Tsubodai, reining in his emotions and shuttering them away so that his eyes were blank. It showed he was more man than boy, but it made him a far more dangerous adversary.

'You may put your faith in me, Tsubodai Bahadur,' Batu said, this time without the sneer in his voice. 'With your permission, I will return to my column.'

Tsubodai inclined his head and Batu trotted his mount back down the goat path that led to the base of the hill. Tsubodai stared after him for a time, then grimaced to himself. He should have sent him back to Karakorum. With any other officer, he would have had him whipped and strapped to a horse to be ridden home in disgrace. Only the memories of Batu's father and, yes, his grandfather held Tsubodai's hand. They had been men to follow. Perhaps the son could be made in their image, unless of course he got himself killed first. He needed to be tested, to gain the soul weight that came only from true knowledge of skill, rather than empty arrogance. Tsubodai nodded to himself as he looked over the lands ahead. There would be many opportunities to temper the young prince in fire. The Russian lands had been wide open for the sort of attack Tsubodai had perfected. Even the nobles there had homes and towns protected by little more than a wooden palisade. Some of them had the solidity of decades or even centuries, but the Mongol war machine had overcome such obstacles in Chin territory. Their catapults smashed apart the ancient logs, sometimes crushing those who sheltered behind them. It was true that the Mongol archers had to contend with thicker forests than they had ever seen, sometimes stretching for thousands of miles and able to hide large forces of horsemen. The last summer had been hot and heavy rainfall meant the ground was often too soft to move forward with any speed. Tsubodai disliked the marshes intensely, but he was coming to the opinion that if it hadn't been for those, Genghis had made an error in attacking to the east. The lands to the west were still ripe, and as yet, Tsubodai had seen no force worthy to challenge his tumans as they scoured the land. The Mongol sweep took them hundreds of miles into the north and winter brought blessed relief from the flies and rain and disease.

For the first year, he had kept to the east of the Volga river, preferring to crush any possible threat from the area that would become his rear and be part of the supply route to Karakorum. Though the distances were vast, there was already a constant stream of riders. The first yam waystations were rising behind his tumans, as well fortified as anything else in Russian territory. Tsubodai cared nothing for the buildings, but they housed grain, saddles and the fastest mounts from the herds, ready for whoever needed to race through.