There was nothing to hear but the wind and the thin mewing of a pair of buzzards high above. Valens watched their flight. They were wheeling, serene on the updrafts, masters of all they surveyed.

The two leaves of the gate swung inwards, making no sound. The hinges must be kept well oiled. A dark passage was revealed, like an entrance to Hades. Valens put away the thought and its foreboding associations as Narses beckoned the wagon forward.

Aulus, up on the box, flicked the whip over the lead horses’ ears. Leaning into their harness, they took the strain so the stones could be removed from under the wheels. Even so, the wagon shifted back half a revolution. Valens and the others seized the spokes, put all their strength and weight against them. Aulus wielded the whip in earnest. The hooves of the draught horses fought for purchase on the flinty surface. For a moment the competing forces held the wagon balanced. Then, with a shuddering groan, it began to edge forward.

The noise of the wagon was deafening under the passageway. Shafts of light penetrated the gloom from the ceiling. Murder holes, Valens thought. From up there the defenders could pour boiling oil or heated sand on any attackers who had managed to force the gate. There was a second gate at the end of the passage. It would not be good to be trapped in the dark between the two.

They emerged into an oval courtyard. Thatched stables were built against the outer wall to the left. The buildings to the right had the air of a barracks. The tower was directly opposite. Valens noted the postern that Narses had mentioned between the tower and the barracks.

The tower itself was some four storeys high. On the upper levels were a few slit windows, all barred. The door was on the first floor. Stone steps ran up flush against the wall. At the top of the flight stood a huge man with a big red beard, dressed entirely in black. There could be no doubt that this was the feared Naduk, the warden of this remote place.

Narses dismounted.

The gates closed behind them. Valens heard the bars drop into place.

The warden began to walk down the steps.

This was the moment of greatest danger. If their intentions were going to be unmasked, it would be now.

Trying to appear casual, even bored, Valens surveyed the courtyard. The two guards were back on the gatehouse. There was a soldier on the north wall, another on the south, and at least one lookout up on the flat roof of the tower. Another look revealed a sixth stationed at the postern gate. Narses had said there were twenty in the garrison. More than a quarter had to stand watch at a time. It would be another reason the posting was unpopular. Despite the chill, some of those off duty were lounging around braziers in front of the barracks.