The fourth man was slow to follow, but as he was the most important of the party – indeed the only man of account among them – Sabinus waited for him to appear. At long last the high transverse crest of the centurion’s helmet came up through the open trap door. Flavius Ferox was another Briton, but he came from a legion, even if currently put in charge of a band of cut-throats. From the start of the tour of the garrison the younger officer had done his best to be amiable. Ferox was senior to him, and by all accounts had a long, even distinguished, record, and it never did any harm to be pleasant to someone who was – or one day might become – a useful acquaintance. Pity the fellow was so surly.

‘The scorpio below,’ Ferox said abruptly before he was even off the ladder, ‘how often is it checked?’ On the level below there was a light bolt-shooting engine, covered as usual against the weather.

Before Sabinus could answer, one of the sentries slammed his boots down on the planking as he came to attention. ‘Cleaned every third day, sir!’ the man shouted his report. ‘Springs checked daily, sir!’

Ferox grunted, and Sabinus hoped that his gratitude to the soldier was not too obvious. He would have remembered the answer eventually, but had gone blank.

‘Can you reach the bridge with it?’ The fort lay beside the main track where it crossed over the river.

‘No,’ Sabinus replied, confident of this at least. ‘With luck and the right wind, you might get close now and again, but not with any accuracy. It’s just over two hundred and fifty paces from the gate to the first plank of the bridge. Two hundred and fifty-three to be precise,’ he added, having supervised the survey himself.

Ferox nodded. ‘So even putting one up here wouldn’t make much difference.’

‘Not really.’

Another grunt, and the centurion climbed off the ladder and stretched. He was a big man, only slightly less tall than the bandit, but broader across the shoulders and giving a sense of brooding power. His eyes were grey and cold, although as he turned his head to look around, Sabinus thought he could see some pleasure. After the best part of two hours spent exploring the buildings and narrow streets of the fort, it was a relief to be up here. Even in the snow the view was magnificent, with the steep valley sides climbing to the north east towards the pass through the mountains and winding away in the opposite direction on the road to the great river.

Sabinus decided that this was a good opportunity to revive everyone’s spirit, so he strode towards the front parapet and waved his arms to gesture at the grandeur around them.

‘Well, there they are,’ he said, his round face more boyish than usual. His helmet, the crest running crosswise like Ferox’s, although in his case black rather than white, seemed too big for him and added to the impression. It was an annoyance wearing the thing on such a routine duty as giving a tour of the fort, but when the senior officer kept his helmet on Sabinus had no choice but to conform.