THE CANYON WAS A DEAD END. If the nomads had followed their tracks, and had seen the discreet signs he had left, when they arrived they would know that the Romans were trapped.

The slopes were no more than forty foot at their highest. They were not so steep that an active man could not scale them with care. But the climber, exposed on the rock face, would be an easy target for an archer. For a man on horseback there was only one way in and out. Some forty paces wide at its entrance, the canyon narrowed to just ten paces towards the far end, where a landslide had fallen from one of the walls. Apart from the jumble of rocks, the floor of the canyon was bare of any cover.

The Romans had corralled their animals behind the ramp of tumbled rocks, but their camp was in front, out in the open, unprotected by the terrain. No sentry had been posted at the entrance to the canyon. Valens had issued the instructions. The arrangement was not ideal – obviously it would have been far better had there been some other way out – but it suited his intentions.

When they had realised that the tent-dwellers were still on their trail, they had moved out quietly, and without fuss. They had ridden through that night, and on into the next afternoon. Daylight had revealed the jagged peaks of the Taurus Mountains ranged ahead, until the foothills closed in on the river valley, and blocked the view. The following day Valens had discarded the first piece of equipment to draw the Arabs after them, and sent Hairan in advance to find the sort of position the Romans now occupied.

There was nothing to do but wait. It would be dawn in an hour or two. Valens sat partly concealed by a boulder from the landslide. Shutting one eye, so as to not ruin his night vision, he squinted at the campfire. By its light he could see the huddled shapes wrapped in cloaks, the glint of metal helmets laid aside, little piles of gear and baggage: a defenceless encampment of the exhausted and unsuspecting.

When he had explained his plan, the men had raised no objections. The nomads were not going to give up. Most likely the Arabs were travelling light, and had spare mounts. The Romans could not outrun them. Something else was necessary.