Before Cato could respond, the sentry thrust his arm out. ‘Sir! Down there!’

Cato turned and followed the direction indicated by the veteran. It took a moment for his eyes to catch the movement and then he saw a figure emerging from the gloom, a man on horseback steadily picking his way across the uneven ground to the avenue of heads before turning his mount up the track towards the gate. Any fleeting satisfaction that Cato felt over Quertus’s misjudgement of the sentry vanished as he scrutinised the approaching rider. Then, when the man was no more than a hundred feet from the ditch, the moon finally broke free of the thin bank of clouds and bathed the night-time landscape in a thin wash of grey light. It was enough to make out some of the details of the approaching rider, and more men moving across the parade ground. Cato felt his heart lurch at the sight of the latter. Then his attention was drawn to the rider again as he reined in and raised something to his lips. A sharp note from a horn split the quiet of the night. The note was repeated again before the rider came on, having alerted the garrison of his intention to talk rather than spring a surprise.

Quertus chuckled and turned to the sentry. ‘Soon as he gets in range, try him with your weapon.’

‘No,’ Cato intervened. ‘He’s played by the rules, so will we. Put aside your javelin.’

The sentry grounded the butt and turned his attention back to the rider.

‘Rules?’ Quertus breathed in deeply.

Cato ignored him and glanced back over the fort. The garrison was fully roused now and light glowed in the doors of the barrack blocks, illuminating men spilling out as they made adjustments to their kits on the way to their assigned stations. Small flames flared as men ran to light the braziers at the foot of each tower to prepare fires to light the tarred bundles of wood that would be thrown out to illuminate the approaches to the fort.

‘You, in the fort!’ a voice called out and Cato fixed his eyes on the rider, approaching the earth-covered trestle bridge that spanned the ditch.

Cato cupped a hand to his mouth. ‘That’s close enough! Stop there!’

The rider obediently reined in and sat tall in his saddle, staring up at the dark outlines of the men atop the gatehouse, black against the backdrop of the stars. Behind and below him, a torch flickered into life close to the parade ground. As the flame caught, other torches were lit and Cato could see a thin line of men stretching out across the ground facing the fort.

‘Who are you and what do you want?’ Cato called down.