Genghis was not more than a few miles to the south when Samuka heard the garrison’s orders echoing inside the walls. He nodded to himself and checked his officers were ready one more time. They were as grim as their general and no one was foolish enough to think they would survive the battle to come.

The iron door in the eastern wall opened slowly. At the same time, ranks of dark bowmen appeared on the walls, thousands of them. Samuka stared up indifferently, judging the numbers. In the days previously, the Mongols had cleared a path to the gate, using pikes to pull down the rubble of charred houses. It had been a good plan at the time, but they had made it easier for the inhabitants to come storming out. Samuka snapped an order and his men readied their bows, placing arrows carefully at their feet where they could be snatched up at speed. One of the makeshift wooden barriers collapsed and Samuka heard an officer swear as he sent men to brace it. Samuka smiled tightly. Genghis had placed him there and he would not be moved easily.

He did not know if the garrison would come at just this one place or try to force Ho Sa’s gate as well, hidden from his sight. Either way, his path was set as he sat his pony just out of range and watched as the iron gates were pushed back. In the sunlit city beyond, ranks of well-armoured men waited on good Arab horses. Samuka squinted at them. They were the ones he had to destroy. Infantry could not reach Genghis in time.

For a man who loved horseflesh, it was a bitter order, but Samuka raised his head. ‘Kill the horses,’ he shouted, his voice carrying far. Like an echo, it was repeated, though with such a small force, there could not have been many who did not hear him. The Mongol ponies were of little use in a crescent formation that could not move, but it was comforting to be in his saddle and Samuka would not have wanted to stand on the ground with an enemy coming at him.

Voices roared in the city and the enemy lunged out. The gateway compressed their ranks, so that only five at a time could hit the gallop. Samuka raised his left hand, looking for the moment. A hundred men bent their bows at the gaps in the barricades. He knew he had to stagger the volleys to conserve the stock of arrows, but he wanted the first one to be terrifying.

The garrison had planned well enough, Samuka saw. They widened their rank as they came through the gate, getting as many men out as possible in the shortest time. Samuka watched impassively as they crossed the marker he had left at a hundred paces.

‘Horses first!’ he shouted again and dropped his hand.

The crack that followed made his heart race. A hundred long shafts soared out, hardly slowing before they hit the emerging horsemen. The first rank collapsed like a burst water-skin, horses and men falling on the dusty ground. Samuka raised his hand again and dropped it almost immediately, knowing the next hundred would be ready. Nothing could resist such hammering blows. Though the Arabs wore armour and carried shields, they fell hard with their horses, then more arrows impaled those who staggered to their feet.

The air above the gates filled with whirring shafts as the archers on the walls bent and loosed. Samuka ducked instinctively, though the barriers protected him. Those that shot high dropped on the shields of his men. They were experienced and took the blows with a light hand, soaking up the impacts.

Still the riders came out. Samuka sent volley after volley at the lines until there were hills of dead men and horses before Otrar. Some of his men were struck by arrows from the walls, but it was only a few.

Lulls came as the garrison used their own wooden barricades to clear the bodies. It took time and the Mongols were pleased to wait before beginning the slaughter once more. Even then, Samuka despaired as he estimated the arrows remaining. If every shot took a life, it would still come to swords in the end.

The brutal exchange went on. If the garrison were willing to ride straight out, Samuka could at least hold them until dark, he was almost sure. His confidence was on the rise when he saw fresh movement on the walls. He glanced up quickly, assuming it was a change of men, or arrows being brought up to them. He grimaced at the sight of ropes spilling over the crest and soldiers clambering down, burning their hands in the need to reach the ground quickly.

Samuka swore, though he had expected it. Already, hundreds were forming up out of his range, and all the time his men sent shafts into the gateway, killing screaming riders as they struggled to break out. Samuka summoned a scout and sent him to Ho Sa on the other side of the city. If the warriors there were still untouched, he could bring a few hundred around and sweep the new threat away. As Samuka watched, more and more ropes became black with climbing men and the ranks on the ground grew thicker and more confident. His heart sank as he saw them begin to run towards his position, swords and shields bright in the afternoon sun. Once more, he dropped his hand to send arrows at riders urging their mounts over their own dead. He could not manoeuvre until the arrows were gone.

If the Otrar officers had decided to take a wide route around him, Samuka would have been forced to cut them off. It was too early to allow them to ride in support of the shah. Samuka watched them carefully, but in his rage and excitement, the governor had clearly ordered them to sweep the Mongols away. They came at the run and Samuka had his mobile five hundred meet them with arrows as they closed, the shafts tearing through their ranks. More and more climbed out of the city and Samuka clenched his jaw in anger and frustration as the first garrison soldiers met his.

While his men fought savagely, four hundred Mongol riders came racing round the city and charged straight at the infantry of Otrar. At first, they cut through them, loosing one vicious wave of shafts before they drew their swords and fell to the killing. The garrison buckled under the onslaught, but every Mongol warrior was met by three or four Arab soldiers. Samuka saw their numbers dwindle as the charge came to a shuddering halt. Assailed on all sides, they fought well and no one broke, but the Arabs cut them down until just a few dozen remained in the press, hacking desperately at anything they could reach. They too fell at last and Samuka groaned aloud as almost ten thousand of the garrison re-formed. He had one last bone to throw and it would not be enough.

Inside the iron gate, he could see lines of fresh cavalry, shouting and holding up their shields. They knew they had the victory.

Wearily, Samuka pulled the silk banner from where he had stuffed it under a saddle cloth. The breeze made it flutter as he raised it over his head. He looked up at the hill behind the city and felt a shadow pass over his face before he heard the crack of the catapults.

Pottery balls shattered against the gate into Otrar, each as large as a man could carry. Samuka held out an arrow with the head bound in oil-soaked cloth and let a warrior light it from a shuttered lamp. He saw two more clay pots break in the gate, sending a horseman tumbling. Samuka sighted carefully and let the arrow go.

He was rewarded by a rush of flame that enveloped the gate and incinerated all those trying to come through it. The Chin fire oil was terrible to see, the heat so intense that many of the Mongol ponies danced back from it until they were brought under control. The catapults on the hill sent more clay pots over the heads of his men, adding to the inferno until the gate itself began to glow dull red. Samuka knew he could ignore the gate for a time. No one could cross those flames and live. He had intended to join Ho Sa on the other side while the first one roared in flames, but the plan had been ruined by the mass of soldiers who had climbed down.