With the sun obscured, it was hard to judge the passing of time.

They came to a forest of ancient oaks. In its depths, moving carefully at a walk, they had altered course to the west.

Once out of the partial shelter of the trees, they had moved back to a canter. The rain had lashed across their path. There was the danger of a horse falling – some slipped, but none went down. Not even the hardiest peasant or shepherd was abroad in the downpour. No one had seen them go, as they fled like creatures of myth from some primordial flood.

As the day ended, the rain slackened but the murk thickened. Narses had turned them once more towards the north, going again at a walk. At the head of the column, the Persian twisted this way and that in his saddle, peering through the spitting rain and the gathering darkness. Sometimes he raised a hand to bring them to a halt. Then he would sit, head titled, listening and sniffing the air.

Fatigue had dulled their thoughts. They sat apathetically in silence, apart from the old eunuch coughing. When Narses moved on, they followed him blindly in the darkness. Few of them noticed when it stopped raining.

It was approaching midnight when the Persian had led the sodden and bedraggled riders through a fringe of reeds and into a grassy hollow, screened from prying eyes. The ground underfoot was damp but firm enough. Narses had urged them to be silent. The Walls of Alexander were less than half a mile away. There were six hours until dawn. They would rest here for four hours, then make their attempt.

The familiar routine of rubbing down his horse – his weight behind the strokes as the brush dried and cleaned its coat, massaged the skin beneath – somehow refreshed his body and cleared his mind. He had sponged its eyes, nose and dock, checked its feet. After he had fed and watered both the animal and himself, Valens had placed him on sentry here at the edge of the reeds.