Tsubodai raised his eyes from the floor, the warning not lost on him.

‘I am loyal, lord. I have always been loyal to you.’

‘I know it,’ Genghis said, gentling his tone with an effort. He knew he did not have the lightness of touch that Kachiun would have brought to the meeting. Genghis rarely thought how he ruled men like Tsubodai, as able as any he had known. In the stillness of the ger, he felt an urge to ease the general’s grief with the right words.

‘Your word is iron, Tsubodai, take pride in that.’

Tsubodai rose and made a stiff bow. His gaze lingered on the sack before he lifted it onto his shoulder.

‘I have to, lord,’ he said. ‘It is all I have left.’

Herat lay almost five hundred miles to the south and west of Samarkand, with two wide rivers and a dozen smaller ones in between. With the gers of the nation on carts, Genghis chose to approach the fortress city from that direction rather than go back to the mountains around Panjshir and strike west through the maze of valleys and hills. Tsubodai and Jebe had gone north from Samarkand, taking Jochi’s tuman and a dark shadow with them. The story of that hunt and death was whispered in a thousand gers, but never when the khan was able to hear.

It was more than two months before the families sighted the orange stone of Herat, a city by a river. It rose from an outcrop of granite and, to Mongol eyes, it was impossibly ancient. On the first raids into the area, Herat had surrendered without bloodshed, preserving the lives of the inhabitants in exchange for tribute and occupation. Kachiun had left a garrison of just eighty men and then forgotten about Herat until the city expelled them, made rash by Jelaudin’s victories.

As Genghis approached it for the first time, he began to appreciate the sheer mass of the fortress. It was built as a square on top of a rock, the walls rising more than a hundred feet from the rugged base, with great round towers set into them at each corner and along their length. He counted twelve towers, each as large as the single one that had sheltered the people of Parwan. It was a huge construction, able to give shelter to thousands racing in ahead of the tumans. Genghis sighed to himself at the sight, knowing from experience that there would be no quick victory. As with Yenking and Yinchuan, he would have to surround it and wait for them to starve.

The gates of the fortress were shut against him, but Genghis sent officers and interpreters to demand surrender as the tumans began to make camp. No answer came and Genghis barely listened as the officers raised a white tent just out of arrow shot. He did not know if the people of Herat knew his rituals and did not care. The white tent would stand for a day, followed by its red twin and then the black cloth that signalled utter destruction for anyone inside the fortress.

It was another two days before the catapults were assembled in front of the walls and the people of Herat remained silent. Genghis wondered if they trusted in their walls or simply understood that he could not accept a peaceful surrender a second time. He waited tensely until the first stones flew, skipping off the orange walls with just a blurred mark to show where they had struck.

The black tent fluttered in the breeze and Genghis relaxed, settling himself for a long siege as he had done many times before. It was his least favourite method of war, but such fortresses had been made to keep out armies like his own and there was no quick solution.

For the nation in the gers, life went on around Herat, punctuated by the rhythmic crack of catapults through each night and day. The families watered their animals at the river, content to leave the destruction of the city to the warriors. The rains had brought sweet grass, though it was already withering in places as the sun beat down. Such concerns were old to them and, if the city did not fall quickly, they would send the herds out to the furthest grazing, leaving the closest hills to be cropped last.

Genghis rested, his wounds having faded to pale scars on his legs and arms. He did not think of Jochi, except with relief that the betrayal had been brought to an end. After Tsubodai had left, the khan had seemed invigorated, willing to fall on Herat with the nation and begin again. His shoulder had healed over time and he rode every day to strengthen his body, ignoring the aches and pains of age. He had sent Chagatai and Kachiun to besiege the city of Balkh in the east, but the main strength of the nation had come with him to the fortress and he took heart from the sight of the encampment. His wife Borte had not spoken to him since she heard the fate of Jochi, but he was oblivious to that. The world lay at his feet and he was strong as he waited for Herat to fall.

In the fourth month of the siege, Genghis was hunting with senior officers around the base of the city. After so long in one place, there were few living things that had escaped the pots of the families. Just a few rabbits remained and they were wary survivors, long used to running from the sound of horse or man.

Balkh had fallen two months before and his tumans had slaughtered the inhabitants, pulling down the stones of the city walls. Only Herat still held out and Genghis was tired of the siege and the hot lands. He had become hopeful of a quick ending when Kachiun and Chagatai returned, but the fortress at Herat was one of the strongest they had ever tried to break.

As the season passed, Genghis had moved his catapults three times, concentrating their stones on flat sections of the walls. Cracks had appeared to great jubilation in the camp, but he sometimes felt he was assaulting a mountain, with as much effect. The walls stood, battered and marked in a thousand places. By then, Genghis knew starvation and thirst would break the city, but he kept his siege weapons working.

‘When this is done, we will go home,’ Genghis muttered to himself, looking up at the walls.

Kachiun and Khasar had heard it a hundred times before from their brother and merely exchanged a glance. A rabbit darted out from cover far ahead of them and all three kicked in their heels to chase it down. Over the noise of hooves, Genghis heard a sharp cry above his head and looked up. There was always someone staring down at his camp from the walls, but this time he saw a man had leaned out too far. The luckless watcher had barely caught himself and now clung to the outer edge by his fingertips. Genghis whistled to his brothers, pointing as the man shouted for help above their heads.

Khasar and Kachiun returned, staring up with interest.

‘A wager?’ Khasar asked. ‘Two horses that he will fall?’

‘Not from me, brother,’ Genghis replied.

There were others reaching down to drag the man back to safety, but he gave a cry of despair as he felt his hands slip. Genghis and his brothers watched in fascination as he tumbled, shrieking as he went. For an instant, it seemed as if an arched stone window might save him. His hands caught on its ledge, but he could not hold on. The brothers winced as he struck the wall again, falling outwards onto the rock base of the fortress. The body spun loosely and came to rest not far away from Genghis. To his astonishment, Genghis saw an arm flail.

‘He’s alive!’ he said.

‘For a few heartbeats, perhaps,’ Khasar replied. ‘That fall would kill anyone.’

Genghis and his brothers trotted over to where the man lay. One of his ankles was clearly broken, the foot twisted. His body was a mass of scrapes and cuts, but he blinked in terror at the generals, unable to believe he had survived.

Khasar drew his sword to finish the man, but Genghis held up a hand.

‘If the spirits won’t kill him after that, we won’t be the ones to do it.’ He looked up in awe at the distance the man had fallen, before addressing the man in halting Arabic.