Tsubodai’s horse almost bolted free at the sight of an empty path ahead. He reined in desperately, knowing that whatever had silenced his men was still waiting. Only one warrior rode ahead of him and that man raced forward madly, calling a war cry and brandishing his sword.

Tsubodai passed through the rubble of the gate and sunlight struck his eyes, almost blinding him. Beyond, he caught a glimpse of a wide spot in the path. His horse was running for it, desperate to get away from the fear and stench of blood in the pass. Tsubodai yanked the reins savagely, turning his mount left as arrows whirred past him. The other warrior had ridden straight in and arrows appeared in his chest. Tsubodai saw him stagger, but his armour held and he had time to kill a bowman before another shaft took him under the chin at close range.

The general gasped for breath, blinking as more warriors clattered out of the pass to join him. Those who had broken arms and collarbones were unable to use their weapons, but they ran into the arrows to clear the pass behind them.

The archers facing them were dressed in white robes, pulled open by the action of drawing their bows. Tsubodai could see they wore the mark of serenity and fury swept over him. He kicked his mount at the massed lines of men. There was nowhere to run or manoeuvre. His warriors would either break the line or die in twos and threes as they came out.

It helped that the horses ran mad with terror. The Mongol warriors hardly tried to stop them as they charged. Tsubodai’s horse went straight at an archer fumbling another arrow onto the string. The shot went buzzing past the general and he swung his sword as he plunged past, his horse kicking the next man down. Tsubodai showed his teeth in cruel pleasure as his warriors began to cut further into the lines. Each man’s chest bristled with arrows, but the armour was good and the archers poor. The Assassins were not warriors, for all the fear they created. They had not trained every day from the moment they could walk. They could not crush fear and pain to make one last cut into an enemy. The warriors of the khan could and did.

The pass ahead was wide enough for five horses to gallop abreast. Perhaps a hundred bowmen stood on tiers of rock, cut almost like steps. They could not hold the flood coming out at them. Volleys might have broken the first ranks, but Tsubodai saw that every man shot alone. He swung his blade at another, cutting a great gash in the man’s side as he whipped past. His horse was foundering, with two arrows deep in its chest. Only its panic kept it running, but Tsubodai was ready when the strength in the animal vanished and it fell hard. He leapt lightly down, staggering almost into the arms of an Arab. Tsubodai spun in a frenzy, so that his sword came round at neck height. The man died and the next he faced was caught helpless between shots. Tsubodai took two sharp strides and plunged his sword into the bare chest, right at the level of the serenity tattoo. A warrior who had come through still mounted kicked out as Tsubodai braced to block a third, sending his intended victim tumbling backwards. Tsubodai looked up in thanks and saw it was Genghis, bloody and jubilant.

Against unarmoured men, Tsubodai thought the archers would have stolen victory even from a large number. The chimney of rock was the best defence he had ever seen and he understood why the Assassins had stayed there to fight. No doubt they thought they could hold against anyone. Tsubodai wiped his mouth, where he tasted something foul and sticky. His hand came away red and he spat on the ground.

Around him, the last of the archers were being cut down and the Mongol riders let out a bellow of victory, releasing all the fear and anger they had not shown before. Tsubodai did not join them. His body was aching from a hundred impacts and he sat down on the stone steps, using his foot to shove away a body and make a space. He found himself panting hard for air, as if his lungs could not fill properly. The sun was high above their heads, not yet even at noon, and Tsubodai laughed weakly at the sight. He felt as if he had been trapped in that dark place for years and every breath was a struggle to find calm.

He looked further up the path, past the warriors and the dead. He had seen the fortress standing over them all the time he had fought, but only now did it enter his thoughts.

The Assassins had made their stronghold from the mountain stones, building it right across the pass so that there was no way around. The cliffs on either side were too smooth to climb and Tsubodai sighed as he studied the single great gate that blocked him still.

‘Hammers here!’ he shouted. ‘Hammers and mantlets.’

The catapults Genghis had brought from Samarkand could not be dragged through the narrow pass, even in pieces. Instead, the work fell to men wielding hammers and wall hooks. The door into the fortress was made of bronze and brass, set well back into stone columns. Progress was incredibly slow and the work was exhausting. Tsubodai organised the hammer teams, with other men bringing up the mantlets so they could work under their protection. By the end of the first day, the columns on both sides of the door were chipped and battered, with great gouges from where iron bars had been struck with hammers. It still held. Above their heads, arrows came at intervals, but the best archers in the nation were standing ready for them, sending shafts up before the Assassins could aim. Even then there were not many defenders and Tsubodai wondered if the main force of the Assassins already lay dead on the bloody steps to the fortress. The Assassins worked best in darkness and with stealth. They did not have the numbers to stand against a determined army, as Genghis had said. All their strength lay in their home never being discovered.

It was a tedious business arranging supplies through the crack in the mountain, but Tsubodai organised torches and food as he relieved his men and fresh warriors took up the task of smashing in the door columns. The archers on the walls had an easier task during the night. They could see the Mongols working, though the mantlets were still held over their heads. Those warriors who passed close to the torchlight risked a sudden arrow humming down at them. As dawn came, seven of Tsubodai’s men had been struck and one holding an iron bar had slipped and had his wrist broken with a hammer. Only three died. The others were dragged back beneath the steps, where they nursed and bound their wounds, waiting for daylight.

As the door held through the morning, Genghis gave orders to level the village of stone behind him. His minghaan officers went back with instructions to knock the stone houses apart and drop them down the cliffs so that more men could use the open space as a staging ground. Almost twenty thousand men waited impotently, unable to reach an enemy while just a few sweated at the wall. Tsubodai seemed confident his men would break in, but as the second day wore on, Genghis had to force the cold face to conceal his impatience.

The Old Man of the Mountains stared down at the armoured soldiers working in the sunlight. He could hardly contain the fury that swept over him. Over the course of his life, he had been honoured by princes and shahs, from the Punjab in India to the Caspian Sea. He demanded respect, even deference, from the few men who knew who he was, without regard for their wealth and blood. His fortress had never been attacked since his ancestor first found the crack in the mountains and formed the clan that would become the most feared force in Arab lands.

The Old Man gripped the stone sill of an open window as he stared out at the ants working to get to him. He cursed the Shah of Khwarezm who had tried to buy the death of this khan, as well as his own fate for taking the man’s note. He had not known then that the shah’s cities would fall to the invader, the stocks of gold with them. He had sent his chosen men to bring down just one, but somehow it had stirred the khan to this desecration. The Old Man had known within days of the failure in Samarkand. His followers had become overconfident, seduced by having the enemy within easy reach. They had died well enough but, in doing so, brought these mindless attackers to his sanctuary.