Tsubodai saw hundreds of foot soldiers gather around a horseman riding a black stallion. Even at a distance, he could see the animal was very fine. Its rider was yelling orders and men formed up with him, making a wedge. Tsubodai braced for a counter-attack, but instead they raised shields and began a fighting retreat back to the main lines.

The Mongol general did not have to give new orders. His minghaan officers were on their own and four of them sensed the withdrawal and raced to attack. Arrows would have slaughtered the retreating soldiers, but there were none left and the Arab ranks stayed together in good order, leaving hills of the dead behind them.

In the distance, Tsubodai heard scout horns moaning across the land. He looked up and saw the tumans of Genghis riding in. The khan had entered the field at last and Tsubodai wiped his eyes of sweat, filled with a terrible pleasure.

His men had shattered those sent against them, but Tsubodai still chafed. The orderly withdrawal had done its work, preventing him from collapsing the lines in on themselves and cutting the head from the shah’s main army. He and his men milled around on the edge of the battle, some still engaged in fighting the last few knots of weary infantry. Tsubodai wondered who the young officer had been who had prevented a complete rout. The man had held his soldiers together in the fire of battle and Tsubodai added the knowledge to what he knew of the enemy. The shah had at least one competent officer under his command, it seemed.

The minghaans re-formed in a landscape of broken men, littered armour and weapons. Some of them dismounted to yank precious arrows out of flesh, but only a few were good enough to be used again. Tsubodai felt his heartbeat settle and took in the battlefield, judging where he was needed. The shah’s army was out of the passes and he could see the tumans of Jebe and Jochi cutting them bloody in the rear. The sun was deep in the west and he thought Genghis would hardly have time to attack before the light faded.

Tsubodai nodded to himself. He could see the last of the shah’s infantry were back on the flank, staring out balefully at the Mongol warriors milling amongst the bodies. Most of the elephants had vanished, though some lay kicking where they had been hit with more arrows from the shah’s own ranks, rather than letting them smash through. Tsubodai was tired and he ached in a dozen places, but the battle was far from over.

‘Form on me!’ he shouted and those who heard responded. As the shah’s ranks marched past, fresh foot soldiers came under Tsubodai’s cold gaze. He could hardly believe it, but the shah’s soldiers were so determined to reach Otrar that they pressed on regardless of the attacking forces.

Tsubodai shook his head. The generals had shown the strength of mobile forces, with the officers acting on their own. Yet the shah’s army lumbered on, holding to a single command no matter what faced them. Tsubodai thought the shah as ruthless as Genghis himself in the way he spent his men.

As Jelme’s men formed with his into columns, Tsubodai saw frightened faces in the shah’s army turn towards him. They knew what was coming, even as he made the decision. He watched them bend their bows and make ready.

Tsubodai reached for the scout’s horn at his neck, only to find it in two pieces, cut by a blow he could not remember. He swore to himself, blind to the grins his words produced in those close by.

‘With me,’ he bellowed. To his left, Jelme’s men dug in their heels and rode.

Genghis had pushed hard for twenty miles to be in that place, changing to fresh mounts when the battle was in sight. He saw the shah had come clear of the hills, but there was no help for that. He looked along the lines to where his son Chagatai galloped and further to Khasar. Fully fifty thousand men rode at his back, with a great tail of spare horses riding behind them. Yet they faced an army that stretched further than he could see. Tsubodai’s flags were barely visible on his left, attacking the flanks. Behind the Arab host, dust clouds roiled and raged. Genghis thought Samuka and Ho Sa would be dead by then, but Otrar was far away and its garrison could not reach the battle that day. He had done all he could, but this was the final fling of the bones. It came to this and he had no other plan except to hit the shah’s column and envelop it in horns.

Genghis snapped an order to a bannerman and heard the fluttering as a gold flag went up. All along the line, thousands of bows creaked. The shah’s army tried to brace for the impact, though their officers urged them on. No one wanted to face these grim warriors again, but there was nowhere to go. They screamed defiance as the gold flag dipped and the air blackened.

The Mongol lines struck at full speed, roaring, the sheer pace as dangerous as the weapons they carried. The wide Mongol horns spilled around the head of the shah’s army, racing along the flanks and cutting in. The light was already grey as the armies met, the sun sinking over the west. The evening was clear and perfect as the Mongols flung themselves at the host of their enemy.

Shah Ala-ud-Din Mohammed cried out in shock as a line of Mongols cut right through to him. His mounted guard slaughtered them to a man, but he was surrounded on all sides and half his army could not bring their weapons to bear. The shah was close to panic as he looked in every direction. It would be dark very soon and yet the Mongols still fought like madmen. They did not make a sound, even when life was ripped from them. The shah could only shake his head at such a display. Did they not feel pain? His son Jelaudin believed they were more like dumb animals than men and he could have been right.

Still the shah’s army moved, staggering as they fought the desire to run from this enemy. Ala-ud-Din saw bright columns of his men being smashed to pieces on the flanks and always the rumble of the Mongols in the rear drove them on.

More and more of the khan’s warriors died as they tried to fight their way to the centre. The shah’s soldiers held formation and cut them to pieces as they came galloping through. They could not match the Mongol speed, but their shields stopped many of the arrows and those who came in were hacked and slashed as they went, sent reeling back time and again. As the light faded, Ala-ud-Din exulted in the enemy dead as his elephant passed over them.

Darkness came and for a time it was a vision of hell. Men cried out as they struggled in a heaving mass of shadows and knives. The shah’s army seemed to be surrounded by a growling djinn, the thunder of hooves in their ears. Soldiers jerked around as they marched on, terrified that the noise of riders was coming straight at them. Above their heads, the stars were clear and bright as the crescent moon rose slowly.

The shah thought that the Mongol khan might continue right to dawn and he prayed constantly as he gave his orders, hoping that he would survive the dark hours. Once again, his guards had to fight off a stray column of raiding warriors, killing eighty or so men and sending the rest galloping away to be cut down by others. The sons of the ancient houses were enjoying themselves, Ala-ud-Din could see. Their teeth flashed as they mimed good cuts to their friends. The army around them was being battered to pieces, but such noble sons would not count those losses. Allah gave and took away as he pleased, after all.

Ala-ud-Din thought dawn would reveal a bloody tatter of the host he had commanded. Only the thought of his enemy suffering as much kept him resolute.

He did not notice the sound dwindle at first. It felt as if he had lived with the thump of hooves in all directions for ever. When it began to fade, he was still calling for his sons, for fresh reports. The army marched on and Otrar would surely be somewhere close before dawn.