Too tired to light a fire, they had sat and eaten cold rations – hard tack and bacon – and drunk sour wine. No one had complained when Valens drew up the rostra of sentries. There were about eight hours of darkness left. Two men would stand guard, one on the lip of the wadi on either side. Each pair would be relieved after two hours. Three men would be on duty in the final session before dawn. Valens took the first watch with Iudex.

After the heat of the day, the temperature dropped fast in the hills at night. Valens was cold, clammy with the sweat from the digging. He had sat, swaddled in his cloak. He had removed his helmet, the better to listen, when a chill breeze blew. He would have liked to pull his hood over his head, but that would have cut down his hearing.

Slowly the vault of stars had wheeled across the sky. The myriad points of distant light made him feel small and alone. Severus was dead. Valens was in command. The weight of responsibility oppressed him. If the gods had been kind he would not have been here . . . But the gods were far away, as distant and uncaring as the stars.

From time to time, the cold and his aching legs and back had forced him to get up and move about. He stepped carefully, his senses alert, probing the darkness. It was quiet. Occasionally a mule had stamped or a horse whickered. A desert fox barked somewhere out in the desolation. There was little to see. If you stared too long at the surrounding slopes, you saw things that were not there. The men and animals were hidden down in the gloom of the depression. On the far bank, the bald head of Iudex gleamed in the light of the stars. The giant man sat motionless, as if lost in meditation.

At long last, a clatter of rocks slipping from under boots climbing the side of the wadi told the watchers that their duty was at an end. Before turning in, Valens had walked the horse lines. The animals had watched him. He paused to stroke their soft muzzles, savour their warm, sweet breath. If you put your face very close to that of a horse, breathe into its nostrils, it will relax and trust you. There was a comfort in animals that was lacking in other men.

Wearily, Valens had struggled out of his armour. It was near impossible to sleep in mail. He tugged off his boots. Using his saddle blanket as a pillow, he had wrapped himself in his cloak, checked his sword was to hand, and fallen asleep.

The trouble started in the morning.

The men must have been talking while Valens still slept.

Aulus, the quartermaster, was their spokesman.

‘We must go back.’

Quintus, the navigator, nodded in agreement.

The others stood in a rough semicircle. Their expressions were impossible to read.