Crispinus pinched the bridge of his nose. ‘I fear that I have a cold. Does it ever get warm in this benighted place?’ He sniffed hard to clear his nostrils. It was a Roman habit Ferox still found strange. ‘People will care,’ he said. ‘Not for the right reasons, but because they will scent weakness. Our Lord Trajan is on the Rhine, and the armies of the two Germanies will most likely stay loyal, but the legions in other provinces do not know him and might be willing to follow someone who promised them wealth to raise him to the purple. It happened when Nero died and that was only thirty years ago, and tens of thousands died in the chaos. It could happen again, very, very easily.’

‘Is that why Trajan – my apologies, our Lord Trajan – is loitering on the German frontier rather than going to Rome to be welcomed by his adoring people? Or is that an impolite question?’ Ferox’s expression gave no hint of repentance.

Crispinus stared at the centurion, who stared back impassively until the tribune gave up and looked away, pretending to follow the flight of a bird. ‘My father was right,’ he said. ‘You have an imaginative and suspicious mind. He said that you did not trust anyone else, but that you followed the scent of the truth like a hound sniffing a trail. Well, he also believed that you can be trusted because of your oath to serve him – and his family, if I am not mistaken.’

Ferox nodded. He had been waiting for Crispinus to remind him of the oath, taken all those years ago on the Danube as the price for convincing the man’s father to march and save some of Ferox’s men.

‘I swore to aid him as long as it did not conflict with my sacramentum, my pledge to Rome and the princeps,’ Ferox said, his voice flat. ‘I am sworn to Trajan and as long as he remains princeps I will keep my word, whatever may happen.’

‘Others may not be so diligent in keeping that same sacred promise of a soldier. There are some who would be happy to make mischief and let our armies be defeated and our soldiers killed simply to discredit the Lord Trajan. They are distinguished men – or friends and dependants of distinguished men – and they may well be in positions of authority. We cannot let them betray the empire and us by engineering defeat.’

They had reached the top of a low rise, and Ferox stopped to stare along the valley ahead of them. He could see pairs of Vindex’s scouts some way ahead and watched as two of the Brigantians paused. Crispinus glanced over his shoulder as Vindex trotted up to join them.

‘Be vigilant and trust no one,’ he whispered to Ferox. ‘If we learn the truth in time then we can stop them.’