Cato and Macro based themselves in the gatehouse, taking turns to walk the defences and ensure that the men were alert. Every so often Cato would pause and stare down into the night, straining his eyes and ears to detect any sign of enemy movement. But there was nothing save the occasional muted order or brief exchange of words from the direction of the parade ground. There was no sign of any activity beyond the other walls of the fort where, in any case, the rush of the river over the rocks made it impossible to pick out any faint sounds. On his return to the gatehouse, Cato laid his helmet to one side and sat against the side of the guardroom. He pulled his cloak tightly about him and closed his eyes. Opposite, Macro snored deeply, until he was roused at the appointed hour to take his turn around the defences. Cato could not sleep, but wanted to show the sentries in the gatehouse that he was confident enough to slumber in the presence of his enemies. It would create a good impression on the men, he knew, and word would quickly spread about the cool-mindedness of the fort’s commander.

But although his head tilted in repose and his chest rose and fell with an easy rhythm, his mind was seething as he went over the layout of the fort and the ground upon which it stood. Then he tried to place himself in the mind of Caratacus and assess the weak points in the defences, and where and how he might assault the fort. For each possibility Cato considered his response and how he might deploy his meagre numbers to hold off the enemy horde. The greatest danger would be if Caratacus unleashed a rolling assault along two or three sides of the fort. That would soon force Cato to commit his reserves and inevitably leave some section of the wall vulnerable. There was one other issue to plague his thoughts. Caratacus would be determined to deal with the fort and its defenders as swiftly as possible, before Ostorius got wind of his location. The garrison could expect an assault at any moment.

As if in answer to his concerns, Cato heard the tramp of boots on the floorboards beside him and a hand shook his shoulder. He hesitated just long enough to give the impression that he was being roused from a deep sleep and then blinked his eyes open and looked up at the dark shape of the duty optio looming over him, barely visible in the wan loom of the single oil lamp burning inside the guardroom.

‘What is it?’

‘Begging your pardon, sir, but one of the lads says he’s heard something in front of the gate.’

Cato gestured across the room to the bulky form of Macro, snorting and rumbling in his slumber. ‘He heard anything above that? Amazing . . . I’ll come.’