The noise intensified to a deep grumbling as Valens launched himself after the older man. Small pebbles and a fine rain of dust fell. The noise reverberated around the vast space. Aulus was at the entrance to the next tunnel when the first boulder crashed into the shelf just behind Valens.

The younger man sprinted, arms pumping, as fast as his legs would go. A small rock glanced off his shoulder. He staggered, almost off balance. The lip of the gorge was horribly close. Another stone caught him between the shoulder blades. He stumbled, then gathered himself and dived after Aulus into the shelter of the outcrop by the next passage.

In the confined space, the avalanche deafened them, stunned their senses. A thick wave of dust surged into the tunnel, gritting their eyes, choking them.

The silence that followed was unnaturally deep. The river was muted. Now it sounded very distant.

Aulus helped Valens to his feet. Valens doubled up, coughing. His hands and knees were grazed, and his back hurt. Aulus picked up the torch the officer had dropped. It had gone out, and he relit it from his own before handing it back.

Together they stepped out from the outcrop and looked back. The dust was dispersing. Most of the rockslide had tumbled down into the abyss. Three substantial boulders had lodged on the shelf, although, thankfully, none of them totally blocked the path.

‘Do you think . . .’

Through Aulus’s words Valens heard a sharp twang. He hurled himself sideways, knocking the soldier to the ground. He felt rather than saw the shaft whip past, heard it snick off the wall of the tunnel.

‘Not a daemon then,’ Aulus said, once they were safely behind the rocks that stuck out like the jamb of a door.

‘Not unless they use a bow and arrow.’ Valens gathered their dropped torches, which were thankfully still alight. ‘I am no expert, but I have never heard of that.’

They were both laughing with shock or relief.

Valens peeked around the entrance to the tunnel, ducking back before their unseen assailant could get his aim. With a sinking heart, the reality of their position dawned on him.

‘There must be a passage down from the galleries. After levering the rocks loose, he has got down between us and the entrance.’

Aulus crawled to glance quickly back along the shelf. Scuttling back, his dusty face was grim. ‘From the opening of that tunnel he can shoot us down if we try to cross the ledge.’

‘Then we are at his mercy.’ Valens heard the note of rising panic in his own voice. ‘We are trapped.’

‘Maybe not,’ Aulus said. He pointed at the flaring torches. The smoke drifted towards the cavern they had left, and ultimately to the entrance to the complex. ‘Stay here, and I will go and find the source of that.’

Valens was seized by a great reluctance to be left alone.