The Persian surged forward to press his advantage. But another horse – the enormous black stallion that had been ridden by the officer – swung around sideways, threatening to dash the puny combatants to the ground with its mountainous shoulders and flanks and haunches. Both men had to scamper out of its way like children.

When the horse was gone, the Persian settled on the balls of his feet, legs close together, sword out two-handed in front.

Leading with his left boot, Valens dropped into the ox guard: half turned, shield well forward of his body, sword held back overhand, its tip level with the rim of the shield.

From all around came the clangour of battle. Off to his right, Valens saw a Persian grabbing at the trailing reins of the black stallion. Steel flashed and rang to his left. This should have been easier. The Persians were outnumbered and surprised. They were unarmoured and had no shields. Yet they were neither running nor being cut down. These warriors were no strangers to standing close to the steel. If they had to die, they intended to sell their lives at a high cost.

Valens advanced cautiously, side on.

The Persian turned slightly, watching his every move.

Two quick, short steps, and Valens rolled his wrist and aimed a high cut at his opponent’s head. The long straight Sassanid blade flicked up. Valens slipped to one knee, altering the angle of strike down to the thigh. The Persian got his blade in the way, moving inside the blow.

Tucking his shoulder inside his shield, with all the strength in his legs, Valens surged upwards at the Persian. Too late, the Persian tried to step back. The boss of Valens’s shield hit him square in the chest. The Persian tottered backwards, arms circling as he fought to steady himself. Valens punched him in the face with the metal boss. Still the man did not fall. Valens hit him again. Now he went down.

On his hands and knees, the Persian scuttled sideways like a crab. Valens brought the heavy blade slicing down into the back of his head. One blow was enough. Planting his boot on the man’s back, Valens wrenched the sword free of the ruined skull.

The back of the officer was just ahead. Narses was still defending himself, but the heels of his boots were right on the edge of the canyon.

The officer must have sensed Valens coming. He sidestepped away from Narses, turning to meet this new threat.

Valens swung first. The officer parried with skill. His riposte got past Valens’s shield. Only a wild twist of his whole body prevented it driving through his armour and skewering his stomach.

Both gathered themselves, shifting on their feet, each searching for an opening.