Ho Sa suffered through a moment of utter weakness. He did not want to die in a land he barely knew. Samuka had given him a chance to live. Khasar looked away rather than watch the turmoil on Ho Sa’s face.

‘I will stay,’ Ho Sa said.

Samuka looked to the skies and blew air out of puffed cheeks.

‘You are a fool then,’ Samuka said. He turned to Khasar and took a deep breath, his manner suddenly brisk. ‘How long must I hold?’

Khasar gave no sign that he had noticed Ho Sa’s struggle.

‘Perhaps a day. I will relieve you myself.’

Both Ho Sa and Samuka bowed their heads, accepting the task before them. On impulse, Khasar reached out and gripped Ho Sa’s shoulder. He had known the Xi Xia officer for many years, ever since the first raids into Chin territory.

‘Stay alive, brother,’ Khasar said. ‘I will come if I can.’

‘I will be watching for you,’ Ho Sa said, his voice rough. His face showed none of the fear that churned in his stomach.

Genghis was already at the head of his army, staring coldly across at the three men. He waited until Samuka shouted orders to five minghaan officers and they rode clear of the main army. Khasar delayed a while to collect four arrows from each warrior of Chagatai’s tuman, passing them on in bundles. Samuka and Ho Sa would need every one. If they could hold the Otrar garrison even until dark, perhaps Genghis would have justified the waste of men.

As the order to remain spread among the five thousand, many heads turned to Khasar. They knew what the orders meant. He sat like a stone and was pleased to see no shouted arguments. They had learned discipline, his people, even unto death.

Genghis dug in his heels and his pony leapt forward. Chagatai and Khasar went with him towards the brown hills where the shah battled the generals. Behind them, the people of Otrar cheered on the walls and only the small, grim force with Samuka and Ho Sa rode back, dwarfed by the city.

The front ranks of the shah’s army marched out of the pass into bright sunlight, roaring at having survived. Arrows had fallen on them in tens of thousands as they forced their way through. Their shields bristled with spent shafts and many of the men used knives to cut them to stubs as they strode on towards Otrar.

Behind them, there was still screaming in the valley as the Mongols tore at the rear of his army, perhaps hoping the Arabs would panic and break. Shah Ala-ud-Din Mohammed smiled grimly at the thought. There was no shame in dying well and his men were strong in their faith. Not one of them had run from the bloody swords of the enemy. The Mongol bows had been silent at the back and that was Allah’s mercy, at least. The shah wondered if they had used up their arrows on Khalifa’s riders, and in his embattled state of mind, he hoped so. It was a better end for the desert thief than betrayal.

It had taken a long time to march through the storm of shafts from Mongols perched like hawks on the cliffs. The sun was long past noon and the shah did not know if the devils would continue their assaults into darkness. Otrar was no more than twenty miles north and he would push his men forward until the city was in sight. He would make his camp where the people of the city would know he had come to save them.

He heard fresh death cries behind and snarled to himself. The Mongols were everywhere, and though his men had locked shields, it was hard to have an enemy killing where you could not see him. His ranks marched on. Only death would stop them reaching the city.

From his high position on the elephant’s back, Ala-ud-Din was among the first to see Tsubodai and Jelme coming out of the mountains on his right side. He cursed under his breath, calling for his noble messengers once more. He cast a quick glance over his army, noting the strengths and regiments to hand, then nodded to the first man to ride close.

‘Tell my son Jelaudin to destroy the flanking force. He may have twelve elephants and ten thousand men under General Faisal. Tell him I will be watching.’

The rider pressed fingers to his lips and heart before racing away to pass on the order. Ala-ud-Din turned his gaze away from the right flank, knowing his son would ride them down.

The shah smiled grimly as his army left the mountain pass behind. Nothing could stop him reaching Otrar. Somewhere ahead, Genghis rode, but he had left it too late. Even if he was on his way, Inalchuk’s garrison would hamstring him. The Mongols were fast and more mobile than Shah Mohammed could believe, but he outnumbered them still and his men would not run while he lived.

It would be a fine battle and Ala-ud-Din was surprised to discover he was looking forward to seeing the khan crushed. It was almost with regret that he had to kill such a daring enemy. The last year had been both exciting and rewarding. He sighed to himself, remembering a childhood tale of a shah who feared black depression almost as much as the giddy heights of overconfidence. When he asked his advisers to find him a solution, they had forged a simple ring with the words ‘This too shall pass’ cut into the gold. There was truth in such simplicity and the shah was content as his battered army strode on to Otrar.

Tsubodai’s columns formed into a wide charging line as they came out of the hills. The head of the shah’s army was already in sight, but Tsubodai halted his men and made them pass arrows to the front ranks. There were very few. He had enough for three quick shots from five hundred men before it was down to swords.

Jelme came to ride at his side as the ponies surged forward.

‘Jochi and Jebe are on the tail of this snake,’ Jelme said. ‘Can we cut off the head?’

‘All things are possible,’ Tsubodai shouted over his shoulder. ‘I can hardly believe this enemy has weathered so many attacks without losing formation. It is one thing more to know, general: they have extraordinary discipline, almost as good as our own. Even with a fool for a leader, they will be hard to break.’

They had just over a mile to ride before they hit the right wing. Tsubodai calculated the time in his head. At that speed, they could reach the lines in two hundred heartbeats.

As they bore down on the army spilling out of the pass, Tsubodai saw a great piece of it break off and face them. He frowned at a line of elephants coming to the fore, jabbed and whipped by their handlers. He felt rather than saw his men hesitate and shouted encouragement to them.

‘The heads are armoured. Aim for the legs,’ he called. ‘Anything that lives can be killed by us.’

Those who heard grinned as the orders flew across the lines. The archers bent their bows in readiness, testing their strength.

The elephants began to lumber forward, picking up speed quickly. Tsubodai saw foot soldiers running alongside them. The elephants were terrifying as they grew and grew before his eyes. Tsubodai readied his sword, swinging it lightly along his horse’s flank, so that it swished the air. He could see the tumans under Genghis coming from the north and wondered idly how the khan had left Otrar at his back.

‘Kill the elephants first!’ he roared to his archers. They were ready and he felt his heartbeat pounding in his chest and throat. The sun was dipping towards the horizon and it was a good day to be alive.

Samuka had arranged his five thousand in two groups at either end of the city, each facing high gates set into the walls. Ho Sa commanded the second and Samuka approved of the cold face the Xi Xia officer had learned in his time with the tribes. Once both men were in position, Samuka became calm. His men had assembled rough barriers braced against rocks that would protect them from arrows while they held the gate. Samuka sighed to himself. Genghis had left him only one advantage and he would use it to the best of his ability. He ran a silk banner through his fingers, enjoying the feel of it. He could see dark faces watching him from the high towers of Otrar and he did not think he would have long to wait.