The Steppe stretched away. It was flatter to the north, utterly without features. There was no cover, just isolated scrubs of wormwood. Nowhere at all to hide. Along the horizon was a series of low, round oddly regular hillocks. They would never reach them.

Their mounts were worn out with hard travel and little rest. Those of the Sassanids must be fresh. Within half an hour the hunters had closed the gap to less than half a mile. They were gaining hand over fist.

Valens could feel the energy dying out of his mount. It was running with its head held to one side, the rhythm of its legs faltering. He bent low over its neck, driving it forward with hands and heels.

There was a shout, then an awful crash from the rear. Valens looked back over his shoulder. Aulus’s horse had fallen. The Gaul had jumped clear. He was down in the dirt. The horse was struggling to rise. One of its front legs was broken.

Decimus, with the spares, was near the front. He did not slacken stride, did not appear to have noticed. Every moment was taking them all further away from Aulus.

High and exultant cries came from the Sassanids just a couple of hundred paces behind.

Valens yanked on his reins, sat back in his seat. He would not leave Aulus alone to die.

The first arrow whistled past to embed itself in the turf.

Suddenly Valens’s mount leapt forward again. The unexpectedness rammed him backwards. Were it not for the rear horns of the saddle, he would have disappeared over the horse’s tail.

‘There is nothing you can do.’ Iudex brought the flat of his sword across the rump of Valen’s mount again. The beast set off, ignoring its rider.

Valens regained his balance, again reined in, and looked back.

Aulus was on his feet, sword drawn.

The Sassanids were almost upon him.

Iudex grabbed Valens’s bridle. ‘Leave him.’

The enemy horsemen were lapping around the solitary man.

‘We will share his fate soon enough.’ Iudex kicked his own horse forward, dragging Valens’s along.

Torn with indecision, Valens let himself be led away.

‘Aulus will buy us a few moments,’ Iudex bellowed. ‘Now ride!’

*

Doing as he was bidden, Valens gazed over his shoulder. Aulus was like a beast at bay. The Gaul turned this way and that. He made little rushes. The horsemen surrounding him wheeled out of range of his blade. The Sassanids did not close with Aulus. Instead they shot him down from a safe distance. The first shaft to hit took him in the back of his thigh. Aulus staggered. The next struck his right arm. He shifted his sword to his left. The third and fourth thumped between his shoulder blades.

Valens looked away, over his horse’s head.

Those strange round hills were not that far away now. But they were bare, and offered nothing except a last stand.